The “unexpected ++” error in jslint [duplicate]

Answer 1

Please note that the ++ operator depends on position with respect to the prior/next variable and the newline / semicolon to determine order of operations.

var a = 1;
var b = a++;
console.log(b); // b = 1
console.log(a); // a = 2

var a = 1;
var b = ++a;
console.log(b); // b = 2
console.log(a); // a = 2

Answer 2

The real problem of the ++ operator is that it is an operator with side effects and thus it is totally opposed to the principle of functional programming.

The "functional" way to implement i++ would be i = i + 1 where you explicitly reassign the variable with no side effects and then use it.

The possibility of confusion is that ++ does two things by adding a value AND reassigning it to the variable.

Answer 3

JSLint friendly loop

for (i = 0; i < 10; i += 1) {
    //Do somthing
}

Answer 4

To avoid confusion, and possible problems when using minifiers, always wrap parens around the operator and its operand when used together with the same (+ or -).

var i = 0, j = 0;
alert(i++ +j);

This adds i and j (and increments i as a side effect) resulting in 0 being alerted.

But what is someone comes along and moves the space?

var i = 0, j = 0;
alert(i+ ++j);

Now this first increments j, and then adds i to the new value of j, resulting in 1 being alerted.

This could easily be solved by doing

var i = 0, j = 0;
alert((i++) +j); 

Now this cannot be mistaken.

Answer 5

Personally, I prefer to put statements such as i++ on a line by themselves. Including them as part of a larger statement can cause confusion for those who aren't sure what the line's supposed to be doing.

For example, instead of:

value = func(i++ * 3);

I would do this:

value = func(i * 3);
i++;

It also means people don't have to remember how i++ and ++i work, and removes the need to apply quite so many preference rules.

Answer 6

Use i += 1 instead, if you want to follow jslint's advice.