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Addition Assignment Operator (+=) (JavaScript)

Adds the value of an expression to the value of a variable and assigns the result to the variable.

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result += expression

Arguments

result: Any variable.
expression: Any expression.

Remarks

Using this operator is exactly the same as specifying:

JavaScript

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result = result + expression

The underlying subtype of the expressions determines the behavior of the += operator.

If	Then
Both expressions are numeric or Boolean	Add
Both expressions are strings	Concatenate
One expression is numeric and the other is a string	Concatenate

Requirements

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards. See Version Information.

Reference

Addition Operator (+) (JavaScript)

Concepts

Operator Precedence (JavaScript)

Operator Summary (JavaScript)

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