+= Operator

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Description

Used to increment a variable by a specified amount.

Syntax

result += expression

The += operator syntax has these parts:

Part	Description
result	Any variable.
expression	Any expression.

Remarks

Use of this operator is exactly the same as specifying:

result = result + expression

The underlying subtype of the expressions determines the behavior of the += operator in the following way:

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.

As for all arithmetic operators, JScript will generate runtime errors for every case in the table below where an E is indicated:

	obj	as	ns	num	bool	undef	null
obj	N	E	N	N	N	E	E
as	E	E	E	E	E	E	E
ns	N	E	N	N	N	E	E
num	N	E	N	N	N	E	E
bool	N	E	N	N	N	E	E
undef	E	E	E	E	E	E	E
null	E	E	E	E	E	E	E

obj = Object, as = Alphanumeric String, ns = Numeric String, num = Number, bool = Boolean, undef = Undefined, null = Null value.