The main assignment operator is a regular equal sign ("="), for instance:

var num = 8;

In combinations with a multiplicative, additive or bitwise-shift operators, the assignment operator becomes a compound assignment operator. These operators are used as shorthand for many situations, such as these:

var num = 8;

num = num + 4;

This example can be re-written as shown here:

var num = 8;

num += 4;

This is the complete list of the compound assignment operators:

  • *= (multiply / assign);
  • /= (divide / assign);
  • %= (modulus / assign);
  • += (add / assign);
  • -= (subtract / assign);
  • < <= (left sign / assign);
  • >>= (signed right shift / assign);
  • >>>= (unsigned right shift / assign);

Example

The example with assignment operators in JavaScript:

​x
 
<!DOCTYPE html>
<html>
<head>
<title>JS tutorial</title>
<style type="text/css">
body {
    margin-top:20px;
    background-color:#eee;
    font-family:"Arial", sans-serif; font-size:0.9em;
}
</style>
<script type="text/javascript">
    var val = 8;
    var mod = 2;
    document.write("<b>Compound assignment operators examples</b>:<br />");
    document.write("<i>note that the value is never reset to initial set point so each following assignment sets the variable to a new value</i><br /><br />");
    document.write("initial value (modifying value): "+val+" ("+mod+")<br />");
    document.write("(value += step): "+(val+=mod)+"<br />");
    document.write("(value -= step): "+(val-=mod)+"<br />");
    document.write("(value *= step): "+(val*=mod)+"<br />");
    document.write("(value /= step): "+(val/=mod)+"<br />");
    document.write("(value %= step): "+(val%=mod)+"<br />");
    document.write("(value &lt;&lt;= step): "+(val<<=mod)+"<br />");
    document.write("(value &gt;&gt;= step): "+(val>>=mod)+"<br />");
    document.write("(value &gt;&gt;&gt;= step): "+(val>>>=mod)+"<br />");
</script>   
​
</head>
<body>
​
</body>
</html>

 

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