Question

In my Javascript code += increments the number but ++ doesn’t. Could somebody explain why?

Doesn’t increment

words[splitted[i]] = ( typeof words[splitted[i]] != 'undefined' ) 
                       ? words[splitted[i]]++ 
                       : 1

Does increment

words[splitted[i]] = ( typeof words[splitted[i]] != 'undefined' ) 
                       ? words[splitted[i]] += 1 
                       : 1

Sample code is here

Answer 1

Your code, in a simpler form, will potentially result in code of this form when words[splitted[i]] is defined:

x = x++;

x++ returns the value of x, and then increments it, and then sets the value returned to x. This contrasts with

x = ++x;

where x is incremented first and then evaluated.

To see how this works, look at the following code:

x = 1;
y = 1;
z = 1;
x = x++;
y = ++y;
z = z += 1;
alert(x); // 1
alert(y); // 2
alert(z); // 2

In any case, I think what you are really wanting to do is something along these lines:

(typeof words[splitted[i]] !== 'undefined') ? 
    words[splitted[i]]++ : 
    words[splitted[i]] = 1;

This is more lines, but might be more readable:

if (typeof words[splitted[i]] !== 'undefined') {
  words[splitted[i]] = 0
}
words[splitted[i]]++;