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
– Michael, Commented Sep 13, 2016 at 6:54
Check console for errors... Array#find expects argument as function, not as value.. — Rayon
– Rayon, Commented Sep 13, 2016 at 6:54
As per @Rayon: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — jedifans
– jedifans, Commented Sep 13, 2016 at 6:55

Community · Accepted Answer · 2020-06-20 09:12:55Z

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, 2020 at 9:12

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answered Sep 13, 2016 at 6:55

illeb

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Comments

T.J. Crowder · Accepted Answer · 2016-09-13 07:20:56Z

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, 2016 at 7:20

answered Sep 13, 2016 at 6:55

T.J. Crowder

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4 Comments

nnnnnn Over a year ago

"or in ES2015" - But you already said that .find() is an ES2015 method...

T.J. Crowder Over a year ago

@nnnnnn: Yes, but it can trivially be polyfilled. I was polyfilling it for fully a year before I started transpiling.

nnnnnn Over a year ago

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).

T.J. Crowder Over a year ago

@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).

Rashad Ibrahimov · Accepted Answer · 2016-09-13 06:56:24Z

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, 2016 at 6:56

Rashad Ibrahimov

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Comments

Paweł Mikołajczyk · Accepted Answer · 2016-09-13 06:56:35Z

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;
};

Comments

T.J. Crowder · Accepted Answer · 2016-09-13 07:14:54Z

2

Try using includes

var foo = ['aaa', 'bbb', 'ccc'];
console.log(foo.includes('aaa'));
console.log(foo.includes('ddd'));

output

true
false

Note: Array#includes wasn't added until ES2016 (in June 2016), so you need a polyfill/shim for even slightly out of date browsers (which is simple, there's one on MDN).

edited Sep 13, 2016 at 7:14

T.J. Crowder

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answered Sep 13, 2016 at 6:59

pius lee

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2 Comments

T.J. Crowder Over a year ago

Good point, includes is a good fit for the "does it exist" use case. But it's important to note that includes wasn't added until June 2016 (e.g., just over two months ago), so you need a polyfill/shim (which is trivial) for even slightly out of date browsers.

nnnnnn Over a year ago

Or foo.includes('aaa') || null to get the true or null result that the OP mentioned in a comment.

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