The JavaScript increment operator adds one to it’s operand. The increment operator can be used either as a prefix or a postfix:
var x = 1;
y = ++x; //Prefix; y is 2
document.write(y);
var x = 1;
y = x++; //Postfix; y is 1
document.write(y);
As seen in the previous example, when the increment operator is applied to a variable prior to the variable evaluation, the variable has the incremented value when evaluated. If the increment operator is applied to a variable after the variable evaluation, the variable is evaluated with the value it contains before it is incremented.
The increment property can be applied on a variable, an array element or a property of an object.
Related articles:
JavaScript Decrement Operator
