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JavaScript Operators

By Stephen Bucaro

An Operator is a charactor or several charactors that cause JavaScript to perform an operation on a value or variable and returns the result of that operation.

Assignment Operators

"Assignment" is when the code actually places a value into a variable. For example the equal sigh below is used to assign the value 2 to the variable nNum.

nNum = 2;

If you want to confuse non-programmers, you can use special shorthand assignment operators that perform a mathematical operation and assign a value at the same time. For example, the code below assigns the value of nNum + 2 to nNum. The value of nNum below will be 5.

nNum = 3;
nNum += 2;

The code below does exactly the same thing.

nNum = 3;
nNum = nNum + 2;

Operator	Alternate Code
nNum -= 3;	nNum = nNum - 3;
nNum *= 3;	nNum = nNum * 3;
nNum ⁄= 3;	nNum = nNum / 3;
nNum %= 3;	nNum = nNum % 3;

Comparison Operators

"Comparison" operators compare the values of two variables or statements and return the result of the comparison as either true or false.

Operator	Comparison
>	greater than
<	less than
==	equal to
!=	not equal to
<=	less than or equal to
>=	greater than or equal to

The result of the comparison can be used to control the flow of the program. The if ⁄ else structure is the most commonly used control structure.

nPrice = 29.00;
nHighest = 32.00;

if(nPrice < nHighest)
{
   document.write("buy it!");
}
else
{
   document.write("don\’t buy it.");
}

In the code shown above, the program would print “buy it.” because the value of nPrice is lower than the value of nHighest. The comparison operator (<) returns true, and the code inside the “if” block is executed.

If the value of nPrice was higher than the value of nHighest, the result of the comparison would be false and the program flow would drop down to the else statement. The program would print "don’t buy it."