Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Operators

Operators in JavaScript, as in PHP, can involve mathematics, changes to strings, and comparison and logical operations (and, or, etc.). JavaScript mathematical operators look a lot like plain arithmetic; for instance, the following statement outputs 15:

document.write(13 + 2)

The following sections introduce the various operators.

Arithmetic Operators

Arithmetic operators are used to perform mathematics. You can use them for the main four operations (addition, subtraction, multiplication, and division), as well as to find the modulus (the remainder after a division) and to increment or decrement a value (see Table 13-2).

Table 13-2. Arithmetic operators

Operator	Description	Example
+	Addition	j + 12
-	Subtraction	j - 22
*	Multiplication	j * 7
/	Division	j / 3.13
%	Modulus (division remainder)	j % 6
++	Increment	++ j
−−	Decrement	−− j

Assignment Operators

The assignment operators are used to assign values to variables. They start with the very simple, =, and move on to +=, -= , and so on. The operator += adds the value on the right side to the variable on the left, instead of totally replacing the value on the left. Thus, if count starts with the value 6, the statement:

count += 1

sets count to 7, just like the more familiar assignment statement:

count = count + 1

Table 13-3 lists the various assignment operators available.

Table 13-3. Assignment operators

Operator	Example	Equivalent to
=	j = 99	j = 99
+=	j += 2	j = j + 2
+=	j += ’string’	j = j + 'string'
-=	j -= 12	j = ...