The Javascript append string operator ( += ) serves two separate purposes in our scripts. First we use it to append to or compund variable data. Secondly we use it is as mathematical shorthand to make the left operand equal to the value of both the right and left operands of the expression.
left_operand += right_operand
Append to a string or variable
Javascript CODE EXAMPLE
var myVar = "<h2>Welcome to my how-to page</h2>";
myVar += "<h3>I Will Explain How To Do This Thing</h3>";
myVar += "<p>First, grab yourself a new clean ...<p>";
myVar += "<p>Second, be sure to insert it firmly into ...<p>";
document.write(myVar);
Simple shorthand arithmetic example
Javascript CODE EXAMPLE
var a = 2;
var b = 3;
document.write(a += b);
