Is there any performance difference using the slice() method with or without the last argument [end]?

Example:

var m = ['But', 'Will', 'It', 'Blend', 'Question'];
var r = m.slice(1,3);

OR

var r = m.slice(2);

PS: not the result as it is, but the performance issue only.

Is there any performance difference using the slice() method with or without the last argument [end]?

Example:

var m = ['But', 'Will', 'It', 'Blend', 'Question'];
var r = m.slice(1,3);

OR

var r = m.slice(2);

PS: not the result as it is, but the performance issue only.

• javascript
• slice

• 1 There is no real difference, and you can test that in jsperf – adeneo Commented Aug 14, 2015 at 11:49
• @adeneo will do. Thank you – lockedz Commented Aug 14, 2015 at 11:50

2 Answers 2

If you take a look at the implementation https://developer.mozilla/en/docs/Web/JavaScript/Reference/Global_Objects/Array/slice you will see that if the second argument is not sent then it uses the array length so no, I think they are the same.

Array.prototype.slice = function(begin, end) {
  // IE < 9 gets unhappy with an undefined end argument
  end = (typeof end !== 'undefined') ? end : this.length;
  .....................................
});

This function has linear plexity (O(n)) in both cases, be it with only one parameter specified, or two. It's the first thing to consider.

The second thing is, in case only one parameter specified, the second one (end of the slice) is being calculated under the hood by default value (#length). So you may think of #slice(4) call as of #slice(4, #length), and these two will be the same.

Next, when the interpreter takes this call and builds an AST around it, it has to deal with two values, not one. So it may seem like twice as time consuming. But pared to the whole script, this overhead is totally negligible.

So, there's no significant difference in timing between the two. It's purely the question of readability of the code.