JavaScript: The Definitive Guide, Fourth Edition

Arithmetic Operators

Having explained operator precedence, associativity, and other background material, we can start to discuss the operators themselves. This section details the arithmetic operators:

Addition (+)

The + operator adds numeric operands or concatenates string operands. If one operand is a string, the other is converted to a string and the two strings are then concatenated. Object operands are converted to numbers or strings that can be added or concatenated. The conversion is performed by the valueOf( ) method and/or the toString( ) method of the object.

Subtraction (-)

When - is used as a binary operator, it subtracts its second operand from its first operand. If used with non-numeric operands, it attempts to convert them to numbers.

Multiplication (*)

The * operator multiplies its two operands. If used with non-numeric operands, it attempts to convert them to numbers.

Division (/)

The / operator divides its first operand by its second. If used with non-numeric operands, it attempts to convert them to numbers. If you are used to programming languages that distinguish between integer and floating-point numbers, you might expect to get an integer result when you divide one integer by another. In JavaScript, however, all numbers are floating-point, so all divisions have floating-point results: 5/2 evaluates to 2.5, not 2. Division by zero yields positive or negative infinity, while 0/0 evaluates to NaN.

Modulo (%)

The % operator computes ...