Missing Doc: Array.prototype.join calls toString internally

[amustaque97]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join

What specific section or headline is this issue about?

Examples

What information was incorrect, unhelpful, or incomplete?

We should demonstrate an example where we tell the readers that if there are nested arrays as items of an array variable If we call the join method on the variable it will internally call toString on the nested array item with , as a delimiter. This will return a flattering array ( which may confuse the users if their delimiter is also comma , ), for example below

Code snippet

const x = ['h', 'e', 'l', 'l', 'o'];

console.log([[[[[[[[x]]]]]]], 'w', 'o', 'r', 'l', 'd'].join(','))

output:

"h,e,l,l,o,w,o,r,l,d" 

What did you expect to see?

Examples like this can be really helpful if someone is a beginner and it can help people during dev or code reviews.

Do you have any supporting links, references, or citations?

Under the spec:
https://tc39.es/ecma262/multipage/indexed-collections.html#sec-array.prototype.join

Read point 7.b

Do you have anything more you want to share?

If we all agree on this, I'm happy to raise an MR.

[Josh-Cena]

I'm not sure what you could add. The fact that "Array.prototype.join calls toString internally" is mentioned on both https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join and https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString. What behavior should it have otherwise, anyway?

[amustaque97]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString

I agree toString page mentions calling the join method but I'm not able to find that line in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join join says it calls toString internally though it only says "new string by concatenating all of the elements in an array" but how it happens we don't tell the reader.

Thoughts?

[Josh-Cena]

Ummm... I see your point. join and toString are mutually recursive. Sure, we can add a sentence or a few examples.

Fun fact: when there's a mutually recursive call you naturally think about what happens when there is a loop:

const a = [];
a[0] = a;
a.join();

And, you will find that none of the browsers get stuck! See tc39/ecma262#289. Before the issue is closed, I don't think we have to mention this edge case; just some food for thought.