Web Design in a Nutshell, 3rd Edition

Arithmetic operators

As you can probably guess, arithmetic operators are used to perform mathematical functions:

    var add      = 1 + 1;   // 2
    var subtract = 7 - 3;   // 4
    var multiply = 2.5 * 2; // 5
    var divide   = 4 / 2;   // 2

These arithmetic operators can also be applied to variables with numeric values:

    var my_num  = 1 + 1;                 // 2
    var new_num = my_num * 5;            // 10
    var my_arr  = Array( 2, new_num );   // an array of numeric values
    var big_num = my_arr[0] * my_arr[1]; // 20

In addition to addition, the + operator has another purpose: concatenation. Concatenation is the combining of two or more values into a new value. It is usually applied to strings:

    var sentence = 'This is one phrase' + ' ' +
                   'and this is another' + '.';

but also applies to combining numbers and strings:

    var new_str = 10 + '20'; // '1020'

Tip

When concatenating numbers with strings, the result is always a string.

There are also a few shorthand arithmetic operators you can use in specific cases, such as having a string or number add to itself:

    var str  = 'Hello there';
        str += ', pilgrim.';  // 'Hello there, pilgrim.'
    var num  = 2;
        num += 2;             // 4

There is a shorthand for incrementing or decrementing a number by one:

    var num = 2;
        num++;   // 3
        num--;   // 2