Find string in array using prototype functions

Question

I have this array:

var str = "rrr";
var arr = ["ddd","rrr","ttt"];

I try to check If arr contains str. I try this:

  var res = arr .find(str);

But on row above is not works any idea what I do wrong?

@Rayon no string exists I expect null if exists I expect true — Michael, Sep 13 '16 at 06:54
Check `console` for errors... `Array#find` expects argument as `function`, not as `value`.. — Rayon, Sep 13 '16 at 06:54
As per @Rayon: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find — jedifans, Sep 13 '16 at 06:55
If, as per your comment, you want a `true` or `null` result depending on whether the item exists (as compared to getting back the index), maybe you should [edit] your question to mention that, because it opens up options like `.includes()`. — nnnnnn, Sep 13 '16 at 07:02
Possible duplicate of [How to find if an array contains a specific string in JavaScript/jQuery?](http://stackoverflow.com/questions/6116474/how-to-find-if-an-array-contains-a-specific-string-in-javascript-jquery) — Makyen, Sep 13 '16 at 07:02
Another time, please use a search engine to at least make an attempt at searching for an answer prior to asking a question. The first result for a Google search for [Find string in array](https://www.google.com/search?q=Find+string+in+array) is a duplicate of your question. — Makyen, Sep 13 '16 at 07:05
If your question is really how to use [Array.prototype.find()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find) then please [edit] your question to reflect that. If that is your question, please explain what it is about the documentation for that method which you don't understand. — Makyen, Sep 13 '16 at 07:08
@Michael: *"no string exists I expect null if exists I expect true"* Why would you want `null` rather than `false`? — T.J. Crowder, Sep 13 '16 at 07:15

score 5 · Answer 1 · edited Jun 20 '20 at 09:12

5

Try using indexOf: it's more widely supported and you can get the same results.

var index = arr.indexOf(str);
if(index != -1) {
  console.log("found");
  var element = arr[index]; //element found of your array
}

Your problem with find function it's probably due to it's compatibility:

As you can see, the chance you are using an incompatible browser it's not so far.

edited Jun 20 '20 at 09:12

Community

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answered Sep 13 '16 at 06:55

illeb

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T.J. Crowder · Accepted Answer · 2016-09-13T07:20:56.323

3

find (added in ES2015, aka "ES6") expects a function predicate. You're looking for indexOf:

var res = arr.indexOf(str);

...which finds things by comparing them with ===. You'll get -1 if it's not found, or its index if it is.

In a comment you've said:

no string exists I expect null if exists I expect true

...which seems a bit odd (I'd think you'd want true or false), but this will give you that:

var res = arr.indexOf(str) != -1 || null;

...because of JavaScript's curiously-powerful || operator (that's a post on my blog).

Just for completeness about find:

But you can use find; ES5 version (in case you're polyfilling but not transpiling):

var res = arr.find(function(entry) { return entry === str; });

or in ES2015:

let res = arr.find(entry => entry === str);

res will be null if it was not found, str if it was. But then, you already have str, so... :-) find is more useful when you're searching for, say, an object by a property value.

edited Sep 13 '16 at 07:20

answered Sep 13 '16 at 06:55

T.J. Crowder

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*"**or** in ES2015"* - But you already said that `.find()` is an ES2015 method... – nnnnnn Sep 13 '16 at 06:59
@nnnnnn: Yes, but it can trivially be polyfilled. I was polyfilling it for fully a year before I started transpiling. – T.J. Crowder Sep 13 '16 at 07:00
1

Fair enough. As always you've covered everything well (though I also upvoted the answer that suggested `.includes()`, because the OP commented above that their desired result is `true` if the item exists and `null` if it doesn't). – nnnnnn Sep 13 '16 at 07:09
@nnnnnn: I did too. I don't see that in the question (and `includes` doesn't return `null` if the item isn't in the array). – T.J. Crowder Sep 13 '16 at 07:11

score 2 · Answer 3 · answered Sep 13 '16 at 06:56

2

It's easy to use simple indexOf method. Just check the documentation.

var array = [2, 9, 9];
array.indexOf(2);     // 0
array.indexOf(7);     // -1
array.indexOf(9, 2);  // 2
array.indexOf(2, -1); // -1
array.indexOf(2, -3); // 0

answered Sep 13 '16 at 06:56

Rashad Ibrahimov

3,279
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score 2 · Answer 4 · answered Sep 13 '16 at 06:56

2

.find method of array prototype expects on input function callback, not string you are looking for.

var res = arr.find(function (element) {
  return element === str;
};

Find string in array using prototype functions

5 Answers5