javascript i++ vs ++i [duplicate]

The difference between i++ and ++i is the value of the expression.

The value i++ is the value of i before the increment. The value of ++i is the value of i after the increment.

Example:

var i = 42;alert(i++); // shows 42alert(i); // shows 43i = 42;alert(++i); // shows 43alert(i); // shows 43

The i-- and --i operators works the same way.

++variable increments the variable, returning the new value.

variable++ increments the variable, but returns the old value.

--variable decrements the variable, returning the new value.

variable-- decrements the variable, but returns the old value.

For example:

a = 5;b = 5;c = ++a;d = b++;

a is 6, b is 6, c is 6 and d is 5.

If you're not using the result, the prefix operators work equally to the postfix operators.

I thought for completeness I would add an answer specific to the first of the OP's question:

One of your example shows the i++ / ++i being used in a for loop :

for (i=1; i<=10; i++) {  alert(i);}

you will get 1-10 in your alerts no matter which you use. Example:

  console.log("i++");  for (i=1; i<=10; i++) {    console.log(i);  }  console.log("++i");  for (i=1; i<=10; ++i) {    console.log(i);  }