7 Core Language

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Example

The second syntactical definition contains the post-decrement operator. This operator is similar to the pre-decrement operator in that it decrements variable by 1. However, the original value is returned by the operation before being decremented.

In both cases, if the operand is a string, it is converted to a number before performing the operation.

Example

Listing 7.16 demonstrates how the pre-decrement and post-decrement operators work. Notice that the variable num holds a string that is converted before performing the decrement operations. The result from executing this code is shown in Figure 7.1.

Listing 7.16 Using the Decrement Operator

Figure 7.1 The difference between pre-decrement and post-decrement.

! (Logical NOT)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

!operand

Description

The ! operator inverts the boolean value returned from the !operand. So, if operand evaluates to true, the result of the operation is false. If the operand evaluates to false, the result is true. When the operand evaluates to a non-Boolean value, it is converted to true or false before performing the inversion.

Example

In Listing 7.17 the character “1” is converted to the Boolean true before inverting the value with the NOT operand. The variable theReverseTruth is assigned false.

Listing 7.17 Using the Logical NOT Operator

!= (Not Equal)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

expression1 != expression2

Description

The not equal operator compares the first expression to the second expression. If the expressions are not equal, true is returned from the operation. If they are equal, false is returned.

JavaScript and Microsoft JScript interpreters attempt to convert the expressions to the same data type before evaluating the not equal operation using the following rules:

• true is converted to the number 1, and false is converted to zero before being compared.

• If either of the operands is NaN, the equality operator returns false.

• Null and undefined are equal.

• Null and undefined are not equal to 0 (zero), "" (empty string), or false.

• If a string and a number are compared, attempt to convert the string to a number and then check for equality.

num1 & num2

Description

The bitwise AND operator looks at the integer numbers on both sides of the operator as 32-bit binary numbers. The bitwise AND (&) operator individually evaluates each of the 32 bits representing the number on the left of the operator to the corresponding bit of the number on the right of the operator using the truth table shown in Table 7.1. The 32-bit binary result of the logical AND operation is converted to an integer value and returned from the bitwise AND operation.

Table 7.1 Bitwise AND Truth Table

Example

The code in Listing 7.22 uses the bitwise AND operator on the numbers 11 and 6. The result of the bitwise AND operation is 2.

Listing 7.22 Using the Bitwise AND Operator

&& (Logical AND)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

expression1 && expression2

Description

The logical AND operator returns true if the expression on the left and the expression on the right of the operator evaluate to true. If either the left, right, or both evaluates to false, the result of the operation is false.

Be sure to note that the implementation of the logical AND operator in JavaScript is more complex than what was just mentioned. The AND operation begins by evaluating the left expression. If the left expression evaluates to false, the basic logic of the AND operator is complete, so the right expression is never evaluated. But if the left expression evaluates to true, the right expression must be evaluated to determine the final result of the AND operation. In either case, the final result returned by the AND operation is actually determined by the result of the last expression to be evaluated.

Example

Listing 7.23 demonstrates the complications associated with the logical AND operator. The first expression evaluates to false, causing the logical AND operation to evaluate to false and the message "The && evaluated FALSE!" is displayed. Because the first expression evaluates to false, the second expression, which assigns the number 5 to the variable x, is not evaluated and x remains equal to 3.

Listing 7.23 The Complicated Logical AND Operator

&= (Bitwise AND Assignment)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

variable &= value

Description

The bitwise AND plus assignment operator looks at the integer numbers on both sides of the operator as 32-bit binary numbers. The bitwise AND (&) operator individually evaluates each of the 32 bits representing the number on the left of the operator to the corresponding bit of the number on the right of the operator using the truth table shown in Table 7.2. The 32-bit binary result of the bitwise AND operation is converted to an integer value and stored in the variable to the left of the operator.

Table 7.2 Bitwise AND Truth Table

Example

The code in Listing 7.35 uses the bitwise OR operator on the numbers 9 and 5. Executing the code displays the number 13 in the browser window.

Listing 7.35 Using the Bitwise OR Operator

|| (Logical OR)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

expression1 || expression2

Description

The logical OR operator returns true if the left operand, right operand, or both operands evaluates to true. If both the operands evaluate to false, the result of the operation is false.

The implementation of the logical OR operator in JavaScript and JScript is more complex than what was just mentioned. The OR operation begins by evaluating the left operand. If the left operand evaluates to true, the basic logic of the OR operator is complete, so the right operand is never evaluated. But if the left operand evaluates to false, the right operand must be evaluated to determine the final result of the OR operation. In either case, the final result returned by the OR operation is actually the result of the last operand to be evaluated.

Example

Listing 7.36 demonstrates the complications associated with the logical OR operator. The first expression evaluates to true, causing the logical OR operation to evaluate to true. Because the first expression evaluates to true, the second expression, which assigns the number 7 to the variable x, is not evaluated so x remains equal to 8.

Listing 7.36 The Complicated Logical OR Operator

|= (Bitwise OR Assignment)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

variable |= value

Description

The bitwise OR assignment operator looks at the integer numbers on both sides of the operator as 32-bit binary numbers. The logical OR (||) operator individually evaluates each of the 32 bits representing the number on the left of the operator to the corresponding bit of the number on the right of the operator. The 32-bit binary result of the logical OR operation is converted to an integer value and stored in the variable on the left of the operator.

Example

Listing 7.37 uses the bitwise OR assignment operator on the numbers 2 and 5 to generate the number 7.

Listing 7.37 Using the Bitwise OR and Assignment Operator

~ (Bitwise NOT)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

~operand

Description

The bitwise NOT operator begins by looking at the number to the right of the operator as a 32-bit binary number. Each bit of the given number is reversed so that all ones become zeros and all zeros become ones. The 32-bit binary result is converted to an integer value and returned from the bitwise NOT operation.

The result of inverting a number can be very confusing because of the way signed numbers are represented. Just remember that applying the bitwise NOT operator to a positive number will return the original number with the sign changed, minus one.

Example

The code in Listing 7.38 demonstrates the use of the bitwise NOT operator. Notice that the result of the operation is -3, which is the original number (2) with the sign reversed (-2) minus 1.

Listing 7.38 The Complicated Bitwise NOT Operator

+ (Addition)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

operand1 + operand2

Description

The addition operator provides two types of functionality depending on the data type of the operands. The first type of functionality is simple addition, in which the value on the left of the addition operator is added to the value on the right. For this type of addition, both operands must be numbers.

The second type of functionality provided by the addition operator is string concatenation. If either of the operands is a string, string concatenation is performed by first converting any non-string operand to a string. String concatenation is then performed by appending the string to the right of the operator to the end of the string located to the left of the operator.

Example

Listing 7.39 demonstrates the addition of numbers as well as string concatenation. Compare the Listing 7.39 to the result of executing the code as seen in Figure 7.2 to understand how addition is handled with various variable types.

Listing 7.39 Addition of Numbers and String Concatenation

Figure 7.2 Using the addition operator to add numbers and concatenate strings.

++ (Increment)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

++variable (Pre-Increment)
variable++ (Post-Increment)

Description

The pre-increment operator increments variable by 1. The new incremented value is returned by the operation.

The post-increment operator is similar to the pre-increment operator in that it increments variable by 1. However, the original value is returned by the operation before being incremented.

In both cases, if the operand is a string, it is converted to a number before performing the operation.

Example

Listing 7.40 demonstrates how the pre-increment and post-increment operators work. Notice that the variable num holds a string that is converted before performing the increment operation. The result of executing this code is shown in Figure 7.3.

Listing 7.40 Using the Increment Operator

Figure 7.3 The difference between pre-increment and post-increment.

+= (Addition Assignment)

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

variable += value

Description

Description

The equal operator compares the value on the left of the operator to the value on the right of the operator. If the values are equal, true is returned from the operation. If the values are not equal, false is returned from the operation.

JavaScript attempts to convert the operands to the same data type before comparing the values for all versions of JavaScript except 1.2. JavaScript adheres to the following rules when performing type conversion:

• True is converted to the number 1, and false is converted to 0 before being compared.

• If either of the operands is NaN, the equality operator returns false.

• Null and undefined are equal.

• Null and undefined are not equal to 0 (zero), "" (empty string), or false.

• If a string and a number are compared, attempts to convert the string to a number and then checks for equality.

ReservedKeyword

Description

The abstract keyword has not been implemented in JavaScript to date, but has been reserved for future use.

Example

This keyword has not been implemented, therefore no example is provided.

ActiveXObject

JScript3.0+

IE4+

Syntax

var variable = new ActiveXObject(serverName.typeName,location)

Description

The ActiveXObject creates a reference to an object that is connected to another application or programming tool through automation interfaces. The arguments used by this object are listed in Table 7.6.

Table 7.6 Arguments Associated with ActiveXObject

Example

Listing 7.56 uses the ActiveXObject to create a multiplication table in a Microsoft Excel document. Excel will be started automatically.

Listing 7.56 Create a Multiplication Table in an Excel Document

Arguments

JavaScript 1.1+, ECMAScript 1E+, JScript 1.0+

Nav3+, IE3+, Opera5+

Syntax

arguments
arguments [index]

Description

The Arguments object is an array that contains all the arguments passed into the currently executing function as well as a few other useful properties. This object is automatically created and initialized when a function is invoked and goes out of scope as soon as the code function finishes executing. To access arguments passed into a function, simply use array brackets to specify an index. Table 7.7 lists the properties associated with the Argument object.

Table 7.7 Properties Associated with the Arguments Object

Although arrays can be created with the basic JavaScript object, the Array object provides a much easier way to create and manage arrays.

Table 7.8 lists the argument and return values associated with this object’s constructors. These constructors create a new array and, in two cases, initialize the Array object based on the arguments passed in the parameter list. The constructor that has no arguments sets the length property to 0.

Table 7.8 Arguments and Return Values Associated with the Array Object

Table 7.9 lists the properties and methods used by the Array object.

Table 7.9 Properties and Methods Used by the Array Object

Example

Listing 7.61 creates an array of numbers using the Array constructor. Once created, the elements are displayed on the screen using bracket notation ([]).

Listing 7.61 Creating an Array and Accessing Its Elements

<html>

<h2>Creating and Accessing Arrays</h2>

<script type=“text/javascript” language=“JavaScript”>

</script>

</html>

Array.concat( )

JavaScript 1.2+, ECMAScript 3E+, JScript 3.0+

Nav4+, NES3+, IE 4+, Opera5+

Syntax

array.concat(arg1,…argN)

Description

The concat() method adds the elements listed in the parameter list to the end of the existing array and returns the result. The original is not changed by this method. Should any of the arguments be Array, the elements of that array are concatenated to the array that called the method.

Table 7.10 lists the argument and return values associated with this method.

Table 7.10 Arguments and Return Values Associated with concat()

Example

Listing 7.62 uses the concat() method to display the total inventory of two grocery store shelves. Notice how the multidimensional arrays wereconcatenated together in Figure 7.4.

Listing 7.62 Using concat() to Display Inventory

Figure 7.4 Concatenate the items on two grocery store shelves.

Array.constructor

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, NES3+, IE4+, ;Opera3+

Syntax

array.constructor

Description

The constructor property of the Array object is used to create the object’s prototype.

Example

Listing 7.63 demonstrates the constructor property as it relates to the Array object.

Listing 7.63 The Array’s constructor Property

Array.index

JavaScript 1.2+, JScript 3.0+ Nav4+, NES3+, IE 4+, Opera4+

Syntax

array.index

Description

The index property is a read-only property that contains the position of a regular expression match within a string. This property only appears in the Array object that is returned from the following regular expression related methods:

• RegExp.exec()

• String.match()

• String.replace()

Example

Listing 7.64 creates a regular expression string that contains the search string “red”.The exec() method is used to find the regular expression within a string. The index property is then used to display "The word red was found at position 4", which contains the position character position (4) within the string where the word “red” was found.

Listing 7.64 Using the index Property to Display the Position of a Match

Array.input

JavaScript 1.2+, JScript 3.0+

Nav4+, NES3+, IE 4+, Opera4+

Syntax

array.input

Description

The input property is a read-only property that contains the string against which the regular expression was matched. This property only appears in the Array object that is returned from the following regular expression related methods:

• RegExp.exec()

• String.match()

• String.replace()

Example

Listing 7.65 creates a regular expression string that contains the search string “red”. The exec() method is used to find the regular expression within a string. The inputproperty is then used to display the string that was searched.

Listing 7.65 Using the index Property to Display the Regular Expression

Array.join()

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, NES3+, IE 4+, Opera3+

Syntax

array.join()
array.join(string)

Description

The join() method converts all the elements of the array to strings and then concatenates all the strings into one string. If an argument is provided in the parameter list, it is used to separate the elements in the string returned by the method. Table 7.11 lists the argument and return values associated with this method.

Table 7.11 Arguments and Return Values Associated with join()

Example

Listing 7.66 creates an array of fruits. The contents of this array are displayed on the screen using the join() method. A dash is specified as the delimiter used to separate the array elements when they are written to the screen as a string.

Listing 7.66 Using the join() Method to Display the Elements of an Array

Array.lastIndex

JavaScript 1.2+, JScript 3.0+

Nav4+, NES3+, IE 4+

Syntax

array.lastIndex

Description

The lastIndex property is a read-only property that contains the position following the last character in a regular expression match. This property only appears in the Array object that is returned from the following regular expression related methods:

• RegExp.exec()

• String.match()

• String.replace()

Example

Listing 7.67 creates a regular expression string that contains the search string “red”. The exec() method is used to find the regular expression within a string. The lastIndex property is then used to display the number 7, which is the position following the word “red” that was found in the string.

Listing 7.67 Using the lastIndex Property to Display the Position Following the Match

Array.length

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, NES3+, IE 4+, Opera3+

Syntax

array.length

Description

The length property holds the number of elements in the array. This property is a read/write variable. If the length property is overwritten with a number that is larger than the original number, new elements are added to the end of the array and assigned undefined values. If the length property is overwritten with a number that is smaller than the original number, elements at the end of the array are lost.

Example

Listing 7.68 creates an array of coins. The number of coins in the array is then reduced from 4 to 3 by modifying the length property so the array contains only three elements. Because the quarter was the last element in the array, it was removed when the length property was changed.

Listing 7.68 Using the length Property to Reduce the Number of Elements in an Array

Array.pop()

JavaScript 1.2+, ECMAScript 3E+, JScript 5.5+

Nav4+, NES3+, IE5.5+, Opera5+

Syntax

array.pop()

Description

The pop()method “pops” elements off the end of the array by deleting the last element of the array and setting the array’s length property to one less than its current value. The element popped off the end of the array is returned from the method. Table 7.12 shows the return value associated with this method.

Table 7.12 Arguments and Return Values Associated with pop()

Example

In Listing 7.69, an array of pages is created to represent a stack of papers. The pop() method removes and returns the top-most paper. After the pop() method is executed, the variable currentPaper contains “Page3”, and the array’s length property is 2.

Listing 7.69 Using the pop() Method to Remove Elements from the End of an Array

Array.prototype

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, NES3+, IE 4+, Opera5+

Syntax

array.prototype.property

Array.prototype.method

Description

The prototype property allows you to add new properties and methods (designated as property/method in the Syntax section) to the Array object that can be used throughout your code.

Example

In Listing 7.70, the prototype property is used to provide a pop() method for working with arrays. Even though a pop() method is already available, a new pop() method will be created. This method overrides the functionality of the Array.pop() method. The new pop() method is used at the end of the code to remove an the “Peach” element from the array of juice flavors. The contents of the flavorArray are displayed before and after the new pop() method is executed to show that the “Peach” flavor was removed.

Listing 7.70 Assigning a New Method to the Array Object with the Prototype Property

Array.push()

JavaScript 1.2+, ECMAScript 3E+, JScript 5.5+

Nav4+, NES3+, IE5.5+, Opera5+

Syntax

array.push (arg1,…argN)

Description

The push() method “pushes” the elements specified in the parameter list on to the end of the array in the order they were listed. Table 7.13 shows the arguments and return values associated with this method.

Table 7.13 Arguments and Return Values Associated with push()

Example

In Listing 7.71, an array of pages is created to represent a stack of papers. The push() method puts two more pages on the end of the array. After the push() method is executed, the variable currentPaper contains “Page4”, and the array’s length property is 4.

Listing 7.71 Using the push() Method to Add Elements to the End of an Array

Array.reverse()

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, NES3+, IE 4+, Opera5+

Syntax

array.reverse()

Description

As mentioned before, if the array should be sorted some other way than jscriptbetically, a function must be provided to handle the new sorting algorithm. The function specified must operate based on the following rules:

• The function must accept two arguments that are to be compared.

• The function must return a number indicating the order of the two arguments in relation to each other.

• If the first argument should appear before the second argument, a number less than zero should be returned from the function.

• If the first argument should appear after the second argument, a number greater than zero should be returned from the function.

• If both arguments are equivalent, zero should be returned from the function.

When the function specified by the sort() method returns zero, signifying that the arguments are equal, the arguments remain in the same order relative to each other after the function has been called.

Example

To help solidify how this method operates, Listing 7.75 demonstrates how to use the method to sort an array based on the number of characters in each argument. Notice how the sort() method changes the order of the elements of the array in Figure 7.5.

Listing 7.75 Sorting an Array Based on Argument Lengths

Figure 7.5 Sort the array elements based on the character length of each element.

Array.splice()

JavaScript 1.2+, ECMAScript 3E+, JScript 5.5+

Nav4+, IE5.5+, Opera5+

Syntax

array.splice(start,delete,arg3,…,argN)

Description

The splice() method provides a way for elements to be either added or deleted from the array. When the delete parameter contains a number other than zero, the elements beginning at start and ending at start+delete are deleted from the array. If delete is zero, no elements are deleted. All elements from start to the end of the array are deleted when delete is not specified. If arguments follow the delete parameter, they are added to the array as elements beginning at the position specified by start. Existing elements are shifted up to allow room for the new elements.

NOTE
There was a bug in Navigator 4 when just one element was deleted from an array. Rather than returning an array that contained the deleted element, the actual element was returned from the method. In addition, when no elements were deleted from the array, null was returned instead of an empty array.

Table 7.17 lists the arguments and return values associated with the splice() method.

Table 7.17 Arguments and Return Values Associated with splice()

Example

To help understand how the splice() method works, Listing 7.76 uses the delete and insert capabilities of the method to simulate a food order at a restaurant. In Figure 7.6, notice how the hamburger was replaced with a hot dog based on the customer’s change in appetite.

Listing 7.76 Using splice() to Simulate a Food Order

Figure 7.6 The food order changed using the splice() method.

Array.toSource()

JavaScript1.3+, JScript3.0

Nav4.06+, IE4

Syntax

array.toSource()

Description

The toSource() method returns one string representing the source of the Array object. The string that is returned contains all the elements in the array separated with commas. The entire string is enclosed with brackets ([]) to show it is an array. If another array is contained within an array, its contents are also part of the string with its own set of brackets.

Example

Listing 7.77 creates an Array object of colors and an Array object of numbers. The array of numbers is included in the array of colors. The toSource() method is then applied to the Array object to return the source string.

[“Blue”, “Green”, “Red”, [3, 6, 7]]

Listing 7.77 Accessing the source of an Array object with the toSource() Method

Array.toString()

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, IE 4+, Opera5+

Syntax

array.toString()

Description

The toString()method returns one string that contains all the elements in the array separated with commas. You might be wondering why anyone would need this method when the join() method can do this and more. The reason is that the toString() method is what JavaScript uses to automatically convert an array to a string when the array is used in string context.

Table 7.18 shows the return value associated with the toString() method.

Table 7.18 Return Value Associated with toString()

Example

Listing 7.78 creates an array of colors and then uses the toString() method to put the contents of the array into a string which is then displayed in the browser.

Listing 7.78 Forcing JavaScript to Use an Array’s toString() Method

Array.unshift()

Syntax

array.unshift(arg1,…argN)

Description

The unshift() method adds the arguments listed in the parameter list to the front of the array as new elements. Existing elements are shifted up to allow room for the new elements. Table 7.19 lists the arguments and return values associated with this method.

Table 7.19 Arguments and Return Values Associated with unshift()

Table 7.20 The Argument, Return Value, Properties, and Methods Associated with the Boolean Object

Example

In Listing 7.83, a Boolean object and a primitive Boolean value are created. There are a couple of key points to notice when examining the results generated by the code, shown in Figure 7.7. First, the Boolean() constructor converts the string “false” to the Boolean value true. Second, boolObj is a Boolean object, whereas boolVal is just a variable holding a primitive Boolean value.

Listing 7.83 A Boolean Object Versus a Primitive Boolean Value

Listing 7.86 creates a Boolean object to represent true. The toSource() method is then applied to the Boolean object to return the source string "(new Boolean(true))".

Listing 7.86 Accessing the Source of a Boolean Object with the toSource() Method

Boolean.toString()

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, IE 4+, Opera5+

Syntax

boolean.toString()

Description

The toString()method returns the string representation (“true” or “false”) of the primitive Boolean value stored in the Boolean object. The return value associated with this object is listed in Table 7.21.

Table 7.21 Return Value Associated with toString()

Example

In Listing 7.87, the toString() method is used to force a comparison of strings rather than Boolean values. Without the toString() method, the if comparison would find the Boolean value not equal to the string value.

Listing 7.87 Force the Desired Comparison Using Boolean ’s toString() Method

Boolean.unwatch()

JavaScript 1.2+

Nav4+, NES3+

Syntax

Boolean.unwatch(property)

Description

The unwatch() method of the Boolean object is used to turn off the watch on a particular property specified by property.

Example

Listing 7.88 shows how the unwatch() method is used to stop watching the user-defined property p.

Listing 7.88 Example of the unwatch() method of the Boolean Object

Boolean.valueOf()

JavaScript1.1+, ECMAScript 1E+, JScript3.0+, Nav3+, NES2+, IE4+, Opera3+

Syntax

boolean.valueOf()

Description

The valueOf() method returns the primitive value of the object. In terms of an instance of a Boolean object, this method returns a Boolean value contained in the object.

Example

Listing 7.89 creates a Boolean object representing true. Because the valueOf() method returns the Boolean value in the object, “true” is written to the browser.

Listing 7.89 Using the valueOf() Method to Return the Value of the Boolean Object

Boolean.watch()

JavaScript 1.2+

Nav4+, NES3+

Syntax

Boolean.watch (property,function)

Description

The watch()method of the Boolean object is used to turn on the watch of a particular property specified by property. Any time the specified property is changed after the watch() method has been called, the specified function is called.

Example

Listing 7.90 shows how the watch() method is used to start watching the user-defined property p.

Listing 7.90 Example of the watch() Method of the Boolean Object

break

JavaScript 1.1+, ECMAScript 1E+, JScript 1.0+

Nav3+, IE 3+, Opera3+

Syntax

break label;

Description

The keyword break provides a way to exit out of loop structures and switch conditionals prematurely. Most of the time, the word break appears on a line by itself, but there are times when a label will follow the keyword (see Table 7.22). When a label is used, code execution completely breaks out of the area designated by label and proceeds to the code that follows the area. To label a statement, simply place the label name followed by a colon (:) in front of the code that needs to be broken out of during code execution.

Table 7.22 Argument Associated with the break Keyword

Example

Listing 7.91 demonstrates the effect of using labels and break statements when working with nested loops. Figure 7.8 shows the result of executing this code.

Listing 7.91 Using break s and Labels

The word class is reserved for future use, so there is no definition at this time.

Example

No example can be provided because class is reserved for future use.

const

JavaScript1.2, ECMAScript 1E+, JScript 5+
Nav4+, NES3+, IE5+, Opera5+

Syntax

Reserved Keyword

Description

The word const is reserved for future use, so there is no definition at this time.

Example

No example can be provided because const is reserved for future use.

continue

JavaScript 1.1+, ECMAScript 1E+, JScript 3.0+

Nav3+, IE 4+, Opera3+

Syntax

continue label;

Description

The continue statement forces the execution of the code within a loop to continue at the beginning of the loop. Normally, the continue keyword appears on a line by itself, but there are times when a label will follow the keyword (see Table 7.23). When a label is used, code execution immediately jumps to the beginning of the loop designated by the label and begins executing code.

Table 7.23 Argument Associated with the continue Keyword

The beginning of a loop varies depending on the type of loop structure. Table 7.24 shows where each looping structure jumps to when a continue structure is encountered.

Table 7.24 Where the continue Statement Jumps

To label a statement, simply place the label name followed by a colon (:) in front of the code where code execution needs to continue.

Example

Listing 7.92 demonstrates the use of labels and continue. This example is a bit complicated, so take time to compare Listing 7.79 to the output in Figure 7.9. Notice how the phrase "Bottom of innerLoop" was not printed after the "Continue at top of innerLoop." because code execution jumped back to beginning of the inner-most loop. When a label was attached to the continue keyword, code execution jumped back to the beginning of the loop labeled outerLoop.

Listing 7.92 Using the continue Statement

Figure 7.9 The result of using the continue statement.

Date

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE 3+, Opera3+

Syntax

var variable = new Date();
var variable = new Date(milliseconds1);
var variable = new Date(string) var variable = new Date(year, month, day, hours, minutes, seconds, milliseconds2)

Description

The Date object represents all aspects of a date and time from year to milliseconds. If arguments are provided when creating the Date object, the new object will contain the date specified; otherwise the object will be set to the current date. The arguments and methods are listed in Table 7.25.

Table 7.25 Arguments and Methods Associated with the Date Object

The getDay()method returns the day of the week expressed as an integer from 0 (Sunday) to 6 (Saturday).

Example

The code in Listing 7.96 uses the getDay() method to return the day of the week expressed as an integer. This number is then converted to a string representation of the day of the week.

Listing 7.96 Using the getDay() Method to Return the Day of the Week

JavaScript 1.2+, ECMAScript 1E+, JScript 3.0+

Nav4+, IE 4+, Opera3+

Syntax

date.getUTCDay()

Description

The getUTCDay() method returns the day of the week converted to universal time and expressed as an integer from 0 (Sunday) to 6 (Saturday).

Example

The code in Listing 7.106 uses the getUTCDay() method to return the day of the week expressed as an integer in universal time. The number is then converted to a string equivalent to the day of the week.

Listing 7.106 Using the getUTCDay() Method to Return the Day of the Week

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Table of Contents for 7 Core Language

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Chapter 7 Core Language

@_alpha

Syntax

Description

Example

@_jscript

Syntax

Description

Example

@_jscript_build

Syntax

Description

Example

@_jscript_version

Syntax

Description

Example

@_mac

Syntax

Description

Example

@_mc680x0

Syntax

Description

Example

@_PowerPC

Syntax

Description

Example

@_win16

Syntax

Description

Example

@_win32

Syntax

Description

Example

@_x86

Syntax

Description

Example

@cc_on

Syntax

Description

Example

@if

Syntax

Description

Example

@set

Syntax

Description

Example

- (Subtraction)

Syntax

Description

Example

- (Unary Negation)

Syntax

Description

Example

-- (Decrement)

Syntax

Description

Example

! (Logical NOT)

Syntax

Description

Example

!= (Not Equal)

Syntax

Description

Example

!== (Non-Identity)

Syntax

Description

Table of Contents for
7 Core Language

**/* / (Multi-line Comment)**