Russ Ferguson and Keith Cirkel
JavaScript RecipesA Problem-Solution Approach
Russ Ferguson
Ocean, New Jersey, USA
Keith Cirkel
London, UK
Any source code or other supplementary materials referenced by the author in this text are available to readers at www.apress.com . For detailed information about how to locate your book’s source code, go to www.apress.com/source-code/ . Readers can also access source code at SpringerLink in the Supplementary Material section for each chapter.
ISBN 978-1-4302-6106-3e-ISBN 978-1-4302-6107-0
DOI 10.1007/978-1-4302-6107-0
Library of Congress Control Number: 2016960744
© Russ Ferguson and Keith Cirkel 2017
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This space is always reserved for my brother Rodd and my Dad. You guys are severely missed.
—Russ
Acknowledgments
There are always a lot of people to thank. Thanks to Keith for letting me help with this project. Thanks to the nice people at Apress, Nancy Chen and Louise Corrigan, who showed a great amount of patience and understanding while this was being made.
Thanks to Luca Mezzalira and James Markham, for looking this over and giving good advice.
I really do appreciate it.
Contents
Chapter 1:​ Working with JavaScript Datatypes 1
Assigning Variables with the var Statement 1
Problem 1
Solution 1
The Code 1
How It Works 1
Solving Errors with Variable Names 2
Problem 2
Solution 2
The Code 3
How It Works 3
Solving Reference Errors When Declaring Variables Inside a Function’s Scope 3
Problem 3
Solution 4
The Code 4
How It Works 4
Assigning Variables with the Let Statement 6
Problem 6
Solution 6
The Code 6
How It Works 7
Assigning Constants with the Const Statement 7
Problem 7
Solution 8
The Code 8
How It Works 8
Creating and Using Literals 8
Problem 9
Solution 9
The Code 9
How It Works 10
Creating Types Using Their Constructors 10
Problem 10
Solution 10
The Code 10
How It Works 11
Determine If a Variable Has Been Defined Using an Equality Operator 11
Problem 11
Solution 11
The Code 11
How It Works 12
Determining If a Variable Has Been Declared Using typeof() 12
Problem 12
Solution 12
The Code 12
How It Works 13
Determining If a Function Defines and Returns a Value 13
Problem 13
Solution 13
The Code 13
How It Works 15
Determining If a Defined Variable Has a Value Using Equality Operators 15
Problem 15
Solution 16
The Code 16
How It Works 17
Performing Operations If a Defined Variable Has a Value 17
Problem 17
Solution 17
The Code 17
How It Works 18
What’s the Difference Between Null and Undefined?​ 18
Problem 18
Solution 18
The Code 19
How It Works 19
Coercing a Boolean Variable Using the Boolean Constructor 19
Problem 19
Solution 19
The Code 20
How It Works 20
Determining If a Boolean Variable Is Initialized 20
Problem 20
Solution 21
The Code 21
How It Works 22
Valid Representations of the False and True Values 22
Problem 22
Solution 22
The Code 22
How It Works 24
Coercing a String Using the String Constructor 24
Problem 24
Solution 24
The Code 24
How It Works 25
Determining If a Variable Is a String 25
Problem 25
Solution 25
The Code 25
How It Works 26
Coercing a Numeric Value Using the Number Constructor 26
Problem 26
Solution 26
The Code 26
How It Works 27
Creating a Numeric Value Using Number Literals 27
Problem 27
Solution 27
The Code 28
How It Works 29
Determining If a Defined Variable Is a Number 29
Problem 29
Solution 29
The Code 29
How It Works 30
Dealing with NaN and Infinity 30
Problem 30
Solution 31
The Code 31
How It Works 32
Generating a Date Using the Date Object 32
Problem 32
Solution 32
The Code 32
How It Works 33
Generating a Date with a Date String 33
Problem 33
Solution 33
The Code 33
How It Works 34
Determining If a Defined Variable Is a Date 34
Problem 34
Solution 35
The Code 35
How It Works 35
Creating an Object and Assigning Properties 36
Problem 36
Solution 36
The Code 36
How It Works 37
Determining If a Defined Variable Is an Object 37
Problem 37
Solution 37
The Code 38
How It Works 38
Determining If an Object Is an Instance 38
Problem 38
Solution 38
The Code 39
How It Works 40
Determining an Object’s Direct Instance with the Constructor Property 40
Problem 40
Solution 40
The Code 40
How It Works 41
Determining If Something Is a Plain Object 42
Problem 42
Solution 42
The Code 42
How It Works 43
Creating an Array and Assigning and Retrieving Values 43
Problem 43
Solution 43
The Code 43
How It Works 44
Choosing Between Objects and Arrays 44
Problem 44
Solution 44
Creating a Regular Expression Literal 45
Problem 45
Solution 45
The Code 45
How It Works 46
Injecting Variables into a String with Template Literals 46
Problem 46
Solution 46
The Code 47
How It Works 47
Chapter 2:​ Working with Expressions 49
Performing an Addition with the + Operator 49
Problem 49
Solution 49
The Code 49
How It Works 50
Performing a Subtraction with the - Operator 50
Problem 50
Solution 50
The Code 50
How It Works 51
Performing Multiplication with the * Operator 51
Problem 51
Solution 51
The Code 51
How It Works 52
Performing Division with the /​ Operator 52
Problem 52
Solution 52
The Code 52
How It Works 52
Getting the Remainder of a Division Operation with the Modulo (%) Operator 53
Problem 53
Solution 53
The Code 53
How It Works 53
Determining If a Value Is Less Than Another with the < Operator 54
Problem 54
Solution 54
The Code 54
How It Works 55
Determining If a Value Is Greater than Another with the > Operator 55
Problem 55
Solution 55
The Code 55
How It Works 56
Determining If a Value Is Less than or Equal to Another with the <=​ Operator 56
Problem 56
Solution 56
The Code 56
How It Works 57
Determining If a Value Is Greater than or Equal to Another with the >=​ Operator 57
Problem 57
Solution 57
The Code 58
How It Works 58
Determining If a Value Is Equivalent to Another Using the =​=​ Operator 59
Problem 59
Solution 59
The Code 59
How It Works 60
Determining If a Value Is Strictly Equal to Another Using the =​=​=​ Operator 62
Problem 62
Solution 62
The Code 62
How It Works 63
Determining If a Value Is Not Equivalent to Another Using the !=​ Operator 64
Problem 64
Solution 64
The Code 65
How It Works 66
Determining If a Value Is Strictly Not Equal to Another Using the !=​=​ Operator 66
Problem 66
Solution 66
The Code 67
How It Works 68
Using the Increment (++) Operator to Increase the Value of a Number Variable 69
Problem 69
Solution 69
The Code 70
How It Works 70
Using the Decrement (--) Operator to Decrease the Value of a Number Variable 70
Problem 70
Solution 71
The Code 71
How It Works 71
Using the Unary Addition (+) Operator to Coerce an Object to a Number 71
Problem 71
Solution 72
The Code 72
How It Works 72
Using the Unary Subtraction (-) Operator to Flip the Sign of a Number 72
Problem 72
Solution 73
The Code 73
How It Works 73
Using the Logical NOT (!) Operator to Toggle a Boolean Value 73
Problem 73
Solution 73
The Code 74
How It Works 74
Deleting an Object, Property, or Array Element with the Delete Operator 74
Problem 74
Solution 74
The Code 75
How It Works 75
Evaluating an Expression Without a Return Value with the Void Operator 76
Problem 76
Solution 76
The Code 76
How It Works 77
Determining the Type of a Variable with the typeof Operator 77
Problem 77
Solution 77
The Code 78
How It Works 78
Using instanceof to Determine If a Variable Is an Instance of an Object 79
Problem 79
Solution 79
The Code 79
How It Works 81
Finding Properties in an Object with the in Operator 81
Problem 81
Solution 81
The Code 82
How It Works 83
Using Logical AND (&​&​) for Combining Boolean Expressions in an if Statement, with Short-Circuit Evaluation 83
Problem 83
Solution 83
The Code 83
How It Works 84
Using Logical OR (||) Short-Circuit Evaluation in an if Statement 84
Problem 84
Solution 84
The Code 85
How It Works 86
Simplifying Variable Assignments Using the Conditional (?​) Operator 86
Problem 86
Solution 86
The Code 86
How It Works 87
Specifying Multiple Expressions Using the Comma Operator 88
Problem 88
Solution 88
The Code 88
How It Works 89
Chapter 3:​ Working with Strings 91
Understanding Unicode Strings 91
Problem 91
Solution 91
The Code 91
How It Works 92
Using Special Characters (Escape Codes) in Strings 93
Problem 93
Solution 93
The Code 93
How It Works 93
Comparing Two Strings for Equality 93
Problem 93
Solution 94
The Code 94
How It Works 94
Determining a String’s Length 95
Problem 95
Solution 95
The Code 95
How It Works 95
Concatenating Strings with the + Operator 96
Problem 96
Solution 96
The Code 96
How It Works 96
Getting a Single Character from a String 97
Problem 97
Solution 97
The Code 97
How It Works 97
Creating a String of UTF Character Code Units with fromCharCode() 98
Problem 98
Solution 98
The Code 98
How It Works 99
Creating a String of UTF Code Points with fromCodePoint() 99
Problem 99
Solution 99
The Code 100
How It Works 100
Getting a Single Character’s UTF Code Unit from a String with charCodeAt() 100
Problem 100
Solution 101
The Code 101
How It Works 101
Getting a Single Character’s UTF Code Point from a string with codePointAt() 102
Problem 102
Solution 102
The Code 102
How It Works 103
Iterating Over a String’s code Units Using for.​.​.​in 103
Problem 103
Solution 103
The Code 103
How It Works 103
Iterating Over a String’s Code Points Using for.​.​.​of 104
Problem 104
Solution 104
The Code 104
How It Works 105
Repeating a String with repeat() 105
Problem 105
Solution 105
The Code 105
How It Works 106
Determining If a String Contains a Smaller String Using contains() 106
Problem 106
Solution 106
The Code 106
How It Works 107
Determining If a String Starts with a Smaller String using startsWith() 108
Problem 108
Solution 108
The Code 108
How It Works 109
Determining If a String Ends with a Smaller String Using endsWith() 110
Problem 110
Solution 110
The Code 110
How It Works 111
Finding the Index of an Occurring Substring with indexOf() 112
Problem 112
Solution 112
The Code 112
How It Works 113
Finding the Index of the Last Occurrence of a Substring with lastIndexOf() 113
Problem 113
Solution 113
The Code 113
How It Works 114
Finding Many Matches of a Substring with match() 114
Problem 114
Solution 114
The Code 115
How It Works 115
Replacing Parts of a String with replace() 115
Problem 115
Solution 115
The Code 116
How It Works 116
Searching a String Using a Regular Expression with search( ) 116
Problem 116
Solution 117
The Code 117
How It Works 117
Getting a Substring Form a String with slice() 118
Problem 118
Solution 118
The Code 118
How It Works 118
Splitting Strings with .​split() 118
Problem 118
Solution 119
The Code 119
How It Works 119
Changing String Case with toUpperCase() and toLowerCase() 120
Problem 120
Solution 120
The Code 120
How It Works 120
Stripping Blank Spaces with trim() 121
Problem 121
Solution 121
The Code 121
How It Works 121
Determining If a String “Comes Before” Another with localeCompare() 122
Problem 122
Solution 122
The Code 122
How It Works 123
Counting the Occurrences of a Substring 123
Problem 123
Solution 123
The Code 124
How It Works 125
Padding a String with a Custom Function 125
Problem 125
Solution 125
The Code 125
How It Works 126
Truncating a String with a Custom Function 127
Problem 127
Solution 128
The Code 128
How It Works 128
Making a ROT13 Cypher with a Custom Function 129
Problem 129
Solution 129
The Code 129
How It Works 130
Calculating the Levenshtein Distance Between Two Strings with a Custom Function 131
Problem 131
Solution 131
The Code 132
How It Works 132
Chapter 4:​ Working with Numbers and Math 137
Converting Strings to Numbers 137
Problem 137
Solution 137
The Code 137
How It Works 138
Creating a Number Object 138
Problem 138
Solution 138
The Code 138
How It Works 138
Checking If a Value Is Not a Number 139
Problem 139
Solution 139
The Code 139
How It Works 139
Formatting a Number to a Fixed Amount of Digits 139
Problem 139
Solution 139
The Code 140
How It Works 140
Checking to See If a Number Is Finite 140
Problem 140
Solution 140
The Code 140
How It Works 141
Checking If a Value Is an Integer 141
Problem 141
Solution 141
The Code 141
How It Works 142
Formatting Numbers for Date Time and Currency 142
Problem 142
Solution 142
The Code 142
How It Works 142
Creating a Random Number Generator 143
Problem 143
Solution 143
The Code 143
How It Works 143
Finding the Absolute Value of a Number 143
Problem 143
Solution 143
The Code 144
How It Works 144
Using Math.​max to Determine the Highest Number 144
Problem 144
Solution 144
The Code 144
How It Works 145
Returning the Square Root of a Number 145
Problem 145
Solution 145
The Code 145
How It Works 145
Using Coercion and Performing Equations 145
Problem 145
Solution 145
The Code 146
How It Works 146
What’s the Difference Between Math.​floor() and Math.​ceil()?​ 146
Problem 146
Solution 146
The Code 147
How It Works 147
Returning a Number in Reverse 147
Problem 147
Solution 147
The Code 147
How It Works 148
Determining the Length of a Number 148
Problem 148
Solution 148
The Code 148
How It Works 148
Swapping Two Numbers Without a Temporary Variable 149
Problem 149
Solution 149
The Code 149
How It Works 149
Chapter 5:​ Working with Bitwise Operations Against 32-Bit Integers 151
What Are 32-Bit Integers?​ 151
Problem 151
Solution 151
The Code 151
How It Works 151
Multiplying by Powers of 2 with the Left Shift (<<) Operator 152
Problem 152
Solution 152
The Code 152
How It Works 152
Dividing by Powers of 2 with the Sign-Propagating Right Shift (>>) Operator 154
Problem 154
Solution 154
The Code 154
How It Works 155
Using the Zero-Fill Right Shift (>>>) Operator to Ensure a Variable Is a 32-Bit Unsigned Integer 156
Problem 156
Solution 156
The Code 156
How It Works 157
Using the Bitwise NOT (~) Operator to Swap All Binary Bits in a 32-Bit Integer 158
Problem 158
Solution 158
The Code 158
How It Works 158
Using Bitwise AND (&​) Operator to Get a Value of All Equal Bits in a 32-Bit Integer 159
Problem 159
Solution 160
The Code 160
How It Works 160
Using Bitwise OR (|) Operator to Get a Value Positive Bits on One or Both Operands 161
Problem 161
Solution 161
The Code 162
How It Works 162
Using the Bitwise XOR (^) Operator to Get a Value of Differing Bits in Each Operand 163
Problem 163
Solution 163
The Code 163
How It Works 164
Converting RGB Color to Hexadecimal and Back Using the Bitwise Signed Shift (>>, <<) Operators and the Bitwise AND (&​) Operator 165
Problem 165
Solution 165
The Code 165
How It Works 166
Creating, Editing, and Testing a Bit Field Flag Set Using Bitwise Operators 169
Problem 169
Solution 169
The Code 169
How It Works 170
Chapter 6:​ Dates and Times 173
Using the Date Object 173
Problem 173
Solution 173
The Code 173
How It Works 173
Getting Date and Time Information 174
Problem 174
Solution 174
The Code 174
How It Works 174
Calculating User Age 175
Problem 175
Solution 175
The Code 175
How It Works 175
Using the HTML5 Date Input Field to Make a Date Object 175
Problem 175
Solution 175
The Code 176
How It Works 176
Checking If Two Dates Are the Same 177
Problem 177
Solution 177
The Code 177
How It Works 177
Working with getTimezoneOffse​t 177
Problem 177
Solution 177
The Code 178
How It Works 178
Formatting Date and Time 178
Problem 178
Solution 178
The Code 179
How It Works 179
Calculating Days from a Certain Date 179
Problem 179
Solution 179
The Code 179
How It Works 180
Checking If Your Date Is in a Range of Dates 180
Problem 180
Solution 180
The Code 180
How It Works 180
Chapter 7:​ Working with Arrays 181
What Is an Array?​ 181
Problem 181
Solution 181
The Code 181
How It Works 181
How Do You Access Elements in an Array?​ 181
Problem 181
Solution 182
The Code 182
How It Works 182
How Do You Create a Multi-Dimensional Array?​ 182
Problem 182
Solution 182
The Code 182
How It Works 182
How Do You Initialize an Array with Values?​ 183
Problem 183
Solution 183
The Code 183
How It Works 183
What Is the Size of the Array?​ 183
Problem 183
Solution 183
The Code 183
How It Works 183
How Do You Convert an Array to a String?​ 184
Problem 184
Solution 184
The Code 184
How It Works 184
How Do You Add an Element to the End of an Array?​ 184
Problem 184
Solution 184
The Code 184
How It Works 185
How Do You Add Items to an Array Within a Range?​ 185
Problem 185
Solution 185
The Code 185
How It Works 185
How Do You Append an Array to the End of Another Array?​ 185
Problem 185
Solution 185
The Code 185
How It Works 186
How Do You Reverse the Order of the Items in an Array?​ 186
Problem 186
Solution 186
The Code 186
How It Works 186
How Do You Copy Elements Based on Their Position Inside an Array?​ 186
Problem 186
Solution 186
The Code 187
How It Works 187
How Do You Add Multiple Items to the Beginning of an Array?​ 187
Problem 187
Solution 187
The Code 187
How It Works 187
How Do You Change the Contents of an Array by Adding or Removing Elements?​ 188
Problem 188
Solution 188
The Code 188
How It Works 188
How Can You Simulate First-In First-Out Behavior?​ 188
Problem 188
Solution 188
The Code 189
How It Works 189
How Can You Simulate Last-In First-Out Behavior?​ 189
Problem 189
Solution 189
The Code 189
How It Works 189
How Do You Create a Smaller Array Based on the Values in a Range?​ 189
Problem 189
Solution 190
The Code 190
How It Works 190
How Do You Get the Index Number of a Value?​ 190
Problem 190
Solution 190
The Code 190
How It Works 190
How Do You Return the Index or Object Based on a Value in an Array?​ 191
Problem 191
Solution 191
The Code 191
How It Works 191
What Is a Spread Operator and How Does It Work?​ 191
Problem 191
Solution 191
The Code 192
How It Works 192
How Do You Take an Iterable Object and Convert It to an Array?​ 192
Problem 192
Solution 192
The Code 192
How It Works 193
How Do Typed Arrays Work and What Makes Them Different from Regular Arrays?​ 193
Problem 193
Solution 193
The Code 193
How It Works 193
Chapter 8:​ Working with Arrays in Loops 195
How Do You Use a for Loop on an Array?​ 195
Problem 195
Solution 195
The Code 195
How It Works 195
How Do You Use a for.​.​.​in Loop with an Array?​ 195
Problem 195
Solution 196
The Code 196
How It Works 196
How Do You Use a for.​.​.​of Loop with an Array?​ 196
Problem 196
Solution 196
The Code 196
How It Works 196
How Do You Loop Through an Array Using do.​.​.​while?​ 197
Problem 197
Solution 197
The Code 197
How It Works 197
How Do You Use a while Loop on an Array?​ 197
Problem 197
Solution 197
The Code 197
How It Works 198
How Do You Sort an Array?​ 198
Problem 198
Solution 198
The Code 198
How It Works 198
How Do You Sort a Multidimensional​ Array?​ 198
Problem 198
Solution 198
The Code 199
How It Works 199
How Do You Run a Function for Each Element in Ascending Order?​ 199
Problem 199
Solution 199
The Code 199
How It Works 200
How Do You Test for a False Condition in an Array?​ 200
Problem 200
Solution 200
The Code 200
How It Works 200
How Do You Test for a True Condition in an Array?​ 200
Problem 200
Solution 200
The Code 201
How It Works 201
How Do You Filter the Elements in an Array?​ 201
Problem 201
Solution 201
The Code 201
How It Works 201
How Can You Reverse Each Word in a String in Place?​ 202
Problem 202
Solution 202
The Code 202
How It Works 202
How Do You Combine the Elements in an Array into a Single Value?​ 202
Problem 202
Solution 202
The Code 203
How It Works 203
What Is the Difference Between reduce and reduceRight?​ 203
Problem 203
Solution 203
The Code 203
How It Works 204
How Do You Find Unique Values in an Array?​ 204
Problem 204
Solution 204
The Code 204
How It Works 204
How Do You Keep Count of Values in an Array?​ 204
Problem 204
Solution 204
The Code 205
How It Works 205
How Do You Get the Max or Min Value in an Array?​ 205
Problem 205
Solution 205
The Code 205
How It Works 205
Chapter 9:​ Working with Objects 207
What Is the Difference Between an Object Constructor and an Object Literal?​ 207
Problem 207
Solution 207
The Code 207
How It Works 207
How Do You Access and Set Properties of an Object?​ 208
Problem 208
Solution 208
The Code 208
How It Works 208
What Is the Difference Between Objects and Arrays?​ 208
Problem 208
Solution 208
The Code 209
How It Works 209
Can You Use Variables to Represent Object Properties?​ 209
Problem 209
Solution 209
The Code 209
How It Works 210
What Does It Mean to Assign Properties of an Object with Metadata?​ 210
Problem 210
Solution 210
The Code 210
How It Works 211
How Do You Get All the Properties from an Object?​ 211
Problem 211
Solution 211
The Code 211
How It Works 212
How Do You Get Just the Enumerable Properties of an Object?​ 212
Problem 212
Solution 212
The Code 212
How It Works 212
How Do You Know If a Property Is Enumerable?​ 212
Problem 212
Solution 212
The Code 213
How It Works 213
How Can You Check If an Object Is a Child or Descendant of Another Object?​ 213
Problem 213
Solution 213
The Code 213
How It Works 214
How Can You Tell If a Property Is on the Current Instance or on the Prototype of an Object?​ 214
Problem 214
Solution 214
The Code 214
How It Works 215
How Do You Copy All Enumerable Values from One or More Objects?​ 215
Problem 215
Solution 215
The Code 215
How It Works 215
What Is the Difference Between Object.​create and Using the New Operator?​ 215
Problem 215
Solution 215
The Code 216
How It Works 216
Can You Change the Prototype of an Object After the Object Has Been Created?​ 216
Problem 216
Solution 216
The Code 216
How It Works 216
How Many Ways Can You Prevent an Object from Being Modified?​ 217
Problem 217
Solution 217
The Code 217
How It Works 218
Can You Check If an Object Is Immutable?​ 218
Problem 218
Solution 218
The Code 218
How It Works 218
Can You Tell If Two Values Are the Same?​ 218
Problem 218
Solution 219
The Code 219
How It Works 219
What Is Object Destructuring?​ 219
Problem 219
Solution 219
The Code 220
How It Works 220
How Do You Loop Through Objects Using a for…in Loop?​ 220
Problem 220
Solution 220
The Code 220
How It Works 221
How Do You Loop Through Objects Using a for…of Loop?​ 221
Problem 221
Solution 221
The Code 221
How It Works 221
How Do You Loop Through Objects Using a do…while loop?​ 222
Problem 222
Solution 222
The Code 222
How It Works 222
How Do You Loop Through Objects Using a while Loop?​ 222
Problem 222
Solution 222
The Code 223
How It Works 223
Chapter 10:​ Working with Sets 225
What Is the Difference Between a Set and an Array?​ 225
Problem 225
Solution 225
The Code 225
How It Works 225
How Do You Add and Remove Elements of a Set?​ 226
Problem 226
Solution 226
The Code 226
How It Works 226
How Do You Remove All the Elements of a Set?​ 226
Problem 226
Solution 226
The Code 226
How It Works 227
What Is the Difference Between the Keys and Values Methods?​ 227
Problem 227
Solution 227
The Code 227
How It Works 227
How Many Elements Are in the Current Set?​ 228
Problem 228
Solution 228
The Code 228
How It Works 228
What Is a WeakSet?​ 228
Problem 228
Solution 228
The Code 228
How It Works 229
How Does a forEach Method Work with a Set Object?​ 229
Problem 229
Solution 229
The Code 229
How It Works 229
Can You Check If an Element Exists in a Set?​ 229
Problem 229
Solution 229
The Code 230
How It Works 230
Can a Set Generate Iterator Objects?​ 230
Problem 230
Solution 230
The Code 230
How It Works 231
Chapter 11:​ Working with Maps 233
What Are the Advantages of Using a Map over an Object?​ 233
Problem 233
Solution 233
The Code 233
How It Works 233
How Do You Add and Remove Elements of a Map?​ 234
Problem 234
Solution 234
The Code 234
How It Works 234
How Do You Remove All the Elements of a Map?​ 234
Problem 234
Solution 234
The Code 234
How It Works 235
How Do You Determine If a Key Exists in a Map?​ 235
Problem 235
Solution 235
The Code 235
How It Works 235
How Do You Get All the Keys of a Map Object?​ 235
Problem 235
Solution 235
The Code 236
How It Works 236
How Do You Get Access to the Value of Each Key Using the Values Method?​ 236
Problem 236
Solution 236
The Code 236
How It Works 237
How Can You Return Both the Key and Value from a Map Object?​ 237
Problem 237
Solution 237
The Code 237
How It Works 237
How Many Elements Are Currently in the Map Object?​ 237
Problem 237
Solution 238
The Code 238
How It Works 238
How Do You Iterate Over a Map Using forEach?​ 238
Problem 238
Solution 238
The Code 238
How It Works 238
Chapter 12:​ Working with Functions 239
How Do You Create a Function?​ 239
Problem 239
Solution 239
The Code 239
How It Works 239
How Do You Call a Function?​ 240
Problem 240
Solution 240
The Code 240
How It Works 240
What Are Anonymous Functions?​ 240
Problem 240
Solution 240
The Code 241
How It Works 241
How Do You Create Functions Inside an Object?​ 241
Problem 241
Solution 241
The Code 241
How It Works 242
How Do You Return a Value from a Function?​ 242
Problem 242
Solution 242
The Code 242
How It Works 242
How Are Parameters Defined in a Function?​ 243
Problem 243
Solution 243
The Code 243
How It Works 243
How Does Using Rest Parameters Allow Unlimited Number of Parameters in a Function?​ 244
Problem 244
Solution 244
The Code 244
How It Works 244
Can You Use Object Destructuring with Parameters of a Function?​ 244
Problem 244
Solution 244
The Code 245
How It Works 245
How Do You Call Methods from an Object’s Parent?​ 245
Problem 245
Solution 245
The Code 245
How It Works 246
How Does the Keyword This Work Inside a Function?​ 247
Problem 247
Solution 247
The Code 247
How It Works 248
Using the Bind Method on a Function 248
Using Call and Apply on a Function 248
Using an Event Handler 248
Using Arrow Functions 249
Using Object Methods 249
What Is the Spread Syntax?​ 249
Problem 249
Solution 249
The Code 249
How It Works 250
What Are Rest Parameters?​ 250
Problem 250
Solution 250
The Code 250
How It Works 251
How Do Arrow Functions Work?​ 251
Problem 251
Solution 251
The Code 252
How It Works 252
What Are Parameter Defaults?​ 253
Problem 253
Solution 253
The Code 253
How It Works 253
Chapter 13:​ Working with Generators 255
How Do You Create a Generator?​ 255
Problem 255
Solution 255
The Code 255
How It Works 255
How Exactly Does Yield Work with a Generator?​ 256
Problem 256
Solution 256
The Code 256
How It Works 256
How Do You Set Up a Generator Function?​ 256
Problem 256
Solution 257
The Code 257
How It Works 257
How Do You Create a Function that Maintains State?​ 257
Problem 257
Solution 257
The Code 257
How It Works 258
How Do You Send Values to a Generator Using the next() Method?​ 258
Problem 258
Solution 258
The Code 258
How It Works 258
Can You Use Throw Inside a Generator?​ 259
Problem 259
Solution 259
The Code 259
How It Works 259
Can You Create a Custom Iterator Inside an Object?​ 260
Problem 260
Solution 260
The Code 260
How It Works 260
How Do You Use a Custom Iterator to Make a Fibonacci Sequence of Numbers?​ 261
Problem 261
Solution 261
The Code 261
How It Works 261
Chapter 14:​ Working with Template Literals 263
How Do You Use Template Literals?​ 263
Problem 263
Solution 263
The Code 263
How It Works 263
Can You Use Template Literals with Functions ?​ 264
Problem 264
Solution 264
The Code 264
How It Works 264
Can You Create Line Breaks with Template Literals?​ 264
Problem 264
Solution 264
The Code 265
How It Works 265
How Do You Use the Raw Property with a Template Literal?​ 265
Problem 265
Solution 265
The Code 265
How It Works 266
Can You Update Expressions Using a Function?​ 266
Problem 266
Solution 266
The Code 266
How It Works 266
Chapter 15:​ Working with Symbols 267
What Are the Advantages of Using Symbols?​ 267
Problem 267
Solution 267
The Code 267
How It Works 267
How Do You Create a Symbol?​ 268
Problem 268
Solution 268
The Code 268
How It Works 268
Can You Access a Symbol by its String Name?​ 268
Problem 268
Solution 268
The Code 269
How It Works 269
Can You Return a Key Based on a Symbol?​ 269
Problem 269
Solution 269
The Code 269
How It Works 269
Can You Use a Symbol as Part of a Function or Method in an Object?​ 269
Problem 269
Solution 270
The Code 270
How It Works 270
How Can a Symbol Override the Constructor Function of Your Custom Class?​ 271
Problem 271
Solution 271
The Code 271
How It Works 271
Can a Constructor Object Recognize an Object as its Instance?​ 271
Problem 271
Solution 272
The Code 272
How It Works 272
Can You Convert an Object to a Primitive Value?​ 272
Problem 272
Solution 272
The Code 272
How It Works 273
How Can You Get the Class of the Object You Are Working With?​ 273
Problem 273
Solution 273
The Code 273
How It Works 274
Can You Hide Properties of an Object?​ 274
Problem 274
Solution 274
The Code 274
How It Works 275
Chapter 16:​ Working with Proxies 277
When Should You Use a Proxy?​ 277
Problem 277
Solution 277
The Code 277
How It Works 277
What Are Traps?​ 278
Problem 278
Solution 278
The Code 278
How It Works 278
What Is the Difference Between Object.​observe and a Proxy?​ 279
Problem 279
Solution 279
How It Works 279
What Is a Revocable Proxy?​ 279
Problem 279
Solution 279
The Code 279
How It Works 280
Chapter 17:​ Working with Classes 281
How Do You Make a Class in JavaScript?​ 281
Problem 281
Solution 281
The Code 281
How It Works 282
How Does the ES6 Class Keyword Work with Prototypal Inheritance?​ 282
Problem 282
Solution 282
The Code 283
How It Works 284
How Do You Assign Getters and Setters to a ES6 Class?​ 284
Problem 284
Solution 284
The Code 284
How It Works 285
What Do the Extend and Super Keywords Do?​ 285
Problem 285
Solution 285
The Code 285
How It Works 286
What Are Static Methods?​ 286
Problem 286
Solution 286
The Code 287
How It Works 287
Chapter 18:​ Working with Events 289
How Do Events Work in JavaScript?​ 289
Problem 289
Solution 289
The Code 289
How It Works 289
How Do Events Propagate Through a Browser?​ 290
Problem 290
Solution 290
The Code 290
How It Works 290
How Do You Create Custom Events in JavaScript?​ 291
Problem 291
Solution 291
The Code 291
How It Works 291
How Do You Remove Event Listeners When They Are No Longer Needed?​ 292
Problem 292
Solution 292
The Code 292
How It Works 292
What Is an Event Emitter in NodeJS?​ 293
Problem 293
Solution 293
The Code 293
How It Works 293
Chapter 19:​ Debugging and Handling Exceptions 295
What Is an Error in JavaScript?​ 295
Problem 295
Solution 295
The Code 295
How It Works 295
What Are the Different Types of Errors?​ 295
Problem 295
Solution 296
The Code 296
How It Works 296
How Can Try/​Catch/​Finally Be Used for Debugging?​ 296
Problem 296
Solution 297
The Code 297
How It Works 297
How Does Throw Work in a Try/​Catch and Can You Rethrow?​ 297
Problem 297
Solution 298
The Code 298
How It Works 298
What Is the Callback Pattern?​ 299
Problem 299
Solution 299
The Code 299
How It Works 299
Can You Create Errors?​ 300
Problem 300
Solution 300
The Code 300
How It Works 300
Chapter 20:​ Working with Regular Expressions 301
What Is a Regular Expression?​ 301
Problem 301
Solution 301
The Code 301
How It Works 301
How Do Regular Expression Flags Work?​ 302
Problem 302
Solution 302
The Code 302
How It Works 302
How Do You Match Literal and Special Characters?​ 302
Problem 302
Solution 303
The Code 303
How It Works 303
How Do You Use Conditions in a Search?​ 303
Problem 303
Solution 303
The Code 303
How It Works 304
How Do You Search for Characters in a Certain Range?​ 304
Problem 304
Solution 304
The Code 304
How It Works 304
How Do You Use Anchors?​ 305
Problem 305
Solution 305
The Code 305
How It Works 305
How Do You Use Matching Quantifiers?​ 306
Problem 306
Solution 306
The Code 306
How It Works 306
What Are Capture Groups?​ 307
Problem 307
Solution 307
The Code 307
How It Works 307
What Are Lookaheads?​ 307
Problem 307
Solution 308
The Code 308
How It Works 308
Chapter 21:​ Working with Asynchronous Control Flow and Promises 309
What Is Asynchronous Control Flow?​ 309
Problem 309
Solution 309
The Code 310
How It Works 310
What Is a Promise?​ 312
Problem 312
Solution 312
How It Works 312
Creating a Promise 318
Problem 318
Solution 318
The Code 319
How It Works 319
Adding Tasks to the Promise Queue with then() 319
Problem 320
Solution 320
The Code 320
How It Works 320
Adding Error Catchers to a then() with the Catch Argument 321
Problem 321
Solution 321
The Code 322
How It Works 322
Adding Error Catchers to the Promise Sequence with catch() 323
Problem 323
Solution 323
The Code 323
How It Works 324
Making an Automatically Fulfilling Promise with Promise.​resolve() 324
Problem 325
Solution 325
The Code 325
How It Works 325
Making an Automatically Rejecting Promise with Promise.​reject() 325
Problem 326
Solution 326
The Code 326
How It Works 326
Working with Multiple Promises in Sequence 327
Problem 327
Solution 327
The Code 327
How It Works 328
Executing Code After the First in a List of Promises Resolves with Promise.​race() 330
Problem 330
Solution 330
The Code 330
How It Works 330
Working with Multiple Promises in Parallel with Promise.​all() 331
Problem 331
Solution 331
The Code 331
How It Works 332
Making a Promise Utility Function that Waits a Given Amount of Time to Fulfill 332
Problem 332
Solution 332
The Code 333
How It Works 333
Making a Promise Utility that Ensures Slow Operations Time Out 334
Problem 334
Solution 334
The Code 334
How It Works 335
Making a Promise Utility that Converts Node-Style Callbacks to Promises 335
Problem 335
Solution 336
The Code 336
How It Works 336
Using Promises with Generators 337
Problem 337
Solution 337
The Code 338
How It Works 338
Index341
About the Authors and About the Technical Reviewer
About the Authors
Russ Ferguson
is a freelance developer and instructor in the New York City area. His interest in computers goes back to Atari Basic, CompuServe, and BBS systems in the mid-1980s. For over 10 years, he has been fortunate to teach at Pratt Institute, where the subjects have been as diverse as the student body. Working in New York has given him the opportunity to work with a diverse group of companies whose projects ranged from developing real-time chat/video applications for startups to developing and managing content management systems for established Media and Advertising agencies like MTV and DC Comics.
 
Keith Cirkel
is a JavaScript Consultant from London, United Kingdom, specializing in writing open source JavaScript libraries and literature. To find out more about his work, visit http://keithcirkel.co.uk , reach him via GitHub at github.com/keithamus , or via Twitter at twitter.com/keithamus .
 
About the Technical Reviewer
Luca Mezzalira
A315054_1_En_BookFrontmatter_Figb_HTML.jpg
is an Italian solutions architect with 13 years of experience, a Google developer expert on web technologies, and the manager of London JavaScript community ( www.londonjs.uk ). He has worked on cutting-edge projects for mobile (iOS, Android, and Blackberry), desktop, web, TVs, set-top boxes, and embedded devices.
He believes the best way to use any programming language is to master its models. He spends much of his time studying and researching topics like OOP, functional programming, and reactive programming. With these skills, he's able to swap easily between different programming languages, applying the best practices learned and driving any team to success.
In his spare time, he writes for national and international technical magazines. He has also tech reviewed for Packt Publishing, Pragmatic Bookshelf, and O'Reilly.
He was a speaker at O'Reilly media webinars, O'Reilly Solutions Architect (San Francisco), O'Reilly Oscon (London), Voxxed Days (Belgrad), JSDay (Verona), CybercomDev (Łódź), Jazoon Conference (Bern), JDays (Göteborg), Codemotion (Milan), FullStack Conference (London), React London UG (London), Node London UG (London), Scrum Gathering (Prague), Agile Cymru (Cardiff), Scotch on the rocks (Edinburgh and London), 360Max (San Francisco), PyCon (Florence), Lean Kanban Conference (London), Flash Camp (Milan), Adobe Creative Suite CS 5.5 - Launch event (Milan), HFWAA (Milan, Turin, Padua, Bari, and Florence), and Mobile World Congress (Barcelona).
 
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