++someVariable vs. someVariable++ in JavaScript

javascript increment unary-operator
Derek Adair picture Derek Adair · Aug 12, 2010 · Viewed 57.8k times · Source

In JavaScript you can use ++ operator before (pre-increment) or after the variable name (post-increment). What, if any, are the differences between these ways of incrementing a variable?

Answer

Jon Skeet picture Jon Skeet · Aug 12, 2010

Same as in other languages:

  • ++x (pre-increment) means "increment the variable; the value of the expression is the final value"
  • x++ (post-increment) means "remember the original value, then increment the variable; the value of the expression is the original value"

Now when used as a standalone statement, they mean the same thing:

x++;
++x;

The difference comes when you use the value of the expression elsewhere. For example:

x = 0;
y = array[x++]; // This will get array[0]

x = 0;
y = array[++x]; // This will get array[1]

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