Add then assign (+=) (Operator/assignment)

Add two numeric operands and assign the result to the first. See concatenation for Strings.

Availability:

ECMAScript edition - 2
JavaScript - 1.0
JScript - 1.0
Internet Explorer - 3.02
Netscape - 2.0
Netscape Enterprise Server - 2.0
Opera - 3.0
Property/method value type:Number primitive
JavaScript syntax:-anOperand1 += anOperand2
Argument list:anOperand1An expression that evaluates to a number
anOperand2Another numeric value

Add the right operand to the left operand and assign the result to the left operand.

This is functionally equivalent to the expression:

anOperand1 = anOperand1 + anOperand2;

Although this is classified as an assignment operator, it is really a compound of an assignment and an additive operator.

It also works with string values and will concatenate the second onto the first.

The associativity is right to left.

Refer to the operator precedence topic for details of execution order.

The new value of anOperand1 is returned as a result of the expression.

Warnings:

Example code:

   // Initialize with numeric values
   myVar1 = 100;
   myVar2 = 1000;
   // After this myVar1 contains 1100, myVar2 is unchanged
   myVar1 += myVar2;

See also:Add (+), Additive operator, Assign value (=), Assignment expression, Assignment operator, Associativity, Concatenate then assign (+=), Increment value (++), LValue, Operator Precedence, Subtract then assign (-=)

Cross-references:

ECMA 262 edition 2 - section - 11.13

ECMA 262 edition 3 - section - 11.13