Assignment and Compound Assignment

     

The assignment operator ( = ) stores the result of an expression in a variable, array element, or object property, as in these examples:

 x = 2; // stores the number 2 in the variable x month[11] = "December";// 12th element of the month array is "December" car.color = 0xFF0000; // color property of car object is 0xFF0000 (red) 

Ten compound assignment operators provide a concise notation for combining the assignment operator with various arithmetic or bitwise operators. For instance, the "add and reassign " operator ( += ) combines assignment and addition. Each compound assignment operator performs an operation on two operands and stores the result in the left operand. For instance, x += 2 adds 2 to x and stores the result in x . This is equivalent to x = x + 2 .

Table A.7 lists the compound assignment operators with examples and equivalent expressions.

Table A.7. Compound Assignment Operators

Name	Operator	Example	Equivalent Expression
add and reassign	+=	i += 2	i = i + 2
subtract and reassign	-=	balance -= debit	balance = balance - debit
multiply and reassign	*=	rate *= increase	rate = rate * increase
divide and reassign	/=	price /= discount	price = price / discount
modulo divide and reassign	%=	frameCounter % slowdown	frameCounter = frameCounter % slowdown
bit-shift left and reassign	<<=	answer <<= num	answer = answer << num
bit-shift right and reassign	>>=	result >>= 1	result = result >> 1
bitwise AND and reassign	&=	test &= 4	test = test & 4
bitwise XOR and reassign	^=	finalMask ^= initialMask	finalMask = finalMask ^ initialMask
bitwise OR and reassign	=	onOff = on	onOff = onOff on

The compound assignment operators are not more efficient computationally than their longer equivalents, nor do they result in smaller SWFs. They are strictly a notational convenience.

Note that

 x *= y + z 

is equivalent to

 x = x * (y + z) 

not

 x = x * y + z 

which is the same as

 x = (x * y) + z