Does a string variable declared in a function get recreated each time the function is called?

Question

If you have a function like:

function test() {
  var hello = "hello world"
}

test();
test();
test();

Will hello variable be recreated three times? Or will the value 'hello world' be stored and the variable will be created but set to point to the same location in memory every time? I'm also asking in the context of modern browsers/JS engines.

I think you would have to refer to the spec for the particular JS Engine implementation. — avrono, Feb 04 '16 at 13:02

Sebastien Daniel · Answer 1 · 2016-02-04T13:10:16.863

yes.

However you could create a IIFE (immediately invoked function expression), that returns a function. That way it wouldn't be re-instantiated every time you call the returned function.

var hi = (function() {
  var hello = "Hello world";

  return function() {
    return hello;
  }
}());

hi(); // "Hello world";

However this could vary depending on which interpreters/JIT compilers you're running on. Some of their optimizations could optimize your code to not re-instantiate every time...

score 2 · Accepted Answer · edited May 23 '17 at 11:59

Will hello variable be recreated three times?

Yes, definitely. (Unless it's completely optimised away by DCE)

Or will the value 'hello world' be stored in the same location in memory every time?

Now that's a different thing - the string value. Since strings are immutable, and the difference between the same value in different memory locations is not observable, we cannot know without looking at the implementation. For that question, see Do common JavaScript implementations use string interning? (hint: yes, they are memory-efficient).

Does a string variable declared in a function get recreated each time the function is called?

2 Answers2