Increments or decrements the value of a variable by one.
The increment and decrement operators are used as a shortcut to modify the value stored in a variable. The value of an expression containing one of these operators depends on whether the operator comes before or after the variable:
var j, k; k = 2; j = ++k;
j is assigned the value 3, as the increment occurs before the expression is evaluated.
Contrast the following example:
var j, k; k = 2; j = k++;
Here, j is assigned the value 2, as the increment occurs after the expression is evaluated.
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