Call forEach on a string in JavaScript

Question

I am not that experienced in JS so maybe this is a very naive question. I tried to call

"".forEach((e, i) => {
    console.log(e)
})

And I get an error saying that forEach is not a function for a string. Yet when I call:

Object.getOwnProperyNames("")

I can clearly see that forEach() is in the prototype of the string and of type function.

Why can I not call it on a string?

You can't use it on a string because it's not available on the String prototype. — Pointy
– Pointy, Commented Aug 25, 2019 at 8:28
I can clearly see that forEach() is in the prototype of the string and of type function. where you can see this, forEach is not available on String — Code Maniac
– Code Maniac, Commented Aug 25, 2019 at 8:30
The array returned from .getOwnPropertyNames() has a .forEach method because it's an array. — Pointy
– Pointy, Commented Aug 25, 2019 at 8:31
What do you expect to be logged in that inner function? Why should a string have a forEach function? — Nico Haase
– Nico Haase, Commented Aug 25, 2019 at 8:33
Sidebar: Isn't Object.getOwnProperyNames("") not the correct way to do this anyway? Shouldn't it be cObject.getOwnPropertyNames(String.prototype)? — Declan McKelvey-Hembree
– Declan McKelvey-Hembree, Commented Aug 25, 2019 at 8:42

Jack Bashford · Accepted Answer · 2019-08-25 08:39:01Z

18

Object.getOwnPropertyNames returns an array, and you can iterate through an array - no surprises there.

As for iterating through a string with a forEach loop, you can't - you can only use a for loop. That is, iterating through a string. A quick and easy way to use forEach is to spread the string into an array:

[..."Hello, World!"].forEach((e, i) => console.log(e));

Or, if it contains certain characters:

Array.from("Hello, World!").forEach((e, i) => console.log(e));

answered Aug 25, 2019 at 8:39

Jack Bashford

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2 Comments

Alex Over a year ago

This works as described in the browser console but I can't get it to compile in my IDE.

GHOST-34 Over a year ago

This is no criticism of the answer, but using the spread operator or Array.from would convert the string to an array via the charAt method, no? Or require a method of iteration for each character in some way. If that's the case, I question the value of performing a duplicate operation that could be done with a single loop.

lealceldeiro · Accepted Answer · 2019-08-25 08:42:04Z

0

Object.getOwnPropertyNames("") only returns ["length"]. The .foreach you're seeing, I assume in Inspector, is a property of the array returned (ie. you could call ["length"].foreach(...)). It does not imply that string has a foreach method.

edited Aug 25, 2019 at 8:42

lealceldeiro

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answered Aug 25, 2019 at 8:38

Declan McKelvey-Hembree

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