Operators take one or two values (or variables), perform an operation, and return a value. Let's check out a simple example of using an operator, just to clarify the terminology:
> 1 + 2;
3
In the preceding code:
- The
+symbol is the operator - The operation is addition
- The input values are
1and2(they are also called operands) - The result value is
3 - The whole thing is called an expression
Instead of using the values 1 and 2 directly in the expression, you can use variables. You can also use a variable to store the result of the operation as the following example demonstrates:
> var a = 1;
> var b = 2;
> a + 1;
2
> b + 2;
4
> a + b;
3
> var c = a + b;
> c;
3
The following table lists the basic arithmetic operators:
|
Operator symbol |
Operation |
Example |
|
|
Addition |
> 1 + 2; 3
|
|
|
Subtraction |
> 99.99 - 11; 88.99
|
|
|
Multiplication |
> 2 * 3; 6
|
|
|
Division |
> 6 / 4; 1.5
|
|
|
Modulo, the remainder of a division |
> 6 % 3; 0 > 5 % 3; 2
It's sometimes useful to test if a number is even or odd. Using the modulo operator, it's easy to do just that. All odd numbers return
> 4 % 2; 0 > 5 % 2; 1
|
|
|
Increment a value by |
Post increment is when the input value is incremented after it's returned, for example: > var a = 123; > var b = a++; > b; 123 > a; 124
The opposite is pre-increment. The input value is incremented by
> var a = 123; > var b = ++a; > b; 124 > a; 124
|
|
|
Decrement a value by 1 |
Post-decrement: > var a = 123; > var b = a--; > b; 123 > a; 122
Pre-decrement:
> var a = 123; > var b = --a; > b; 122 > a; 122
|
The var a = 1; is also an operation; it's the simple assignment operation, and = is the simple
assignment
operator.
There is also a family of operators that are a combination of an assignment and an arithmetic operator. These are called compound operators. They can make your code more compact. Let's see some of them with the following examples:
> var a = 5;
> a += 3;
8
In this example, a += 3; is just a shorter way of doing a = a + 3;. For example:
> a -= 3;
5
Here, a -= 3; is the same as a = a - 3;:
> a *= 2;
10
> a /= 5;
2
> a %= 2;
0
In addition to the arithmetic and assignment operators discussed previously, there are other types of operators, as you'll see later in this, and the following chapters.
Note
Best practice
Always end your expressions with a semicolon. JavaScript has a semicolon insertion mechanism, where it can add the semicolon if you forget it at the end of a line. However, this can also be a source of errors, so it's best to make sure you always explicitly state where you want to terminate your expressions. In other words, both expressions > 1 + 1 and > 1 + 1; will work; but throughout the book, you'll always see the second type, terminated with a semicolon, just to emphasize this habit.