javascript array.find() object undefined?

Question

Why is the object undefined, if I call it in arr.find with 'this'?

let o = { name: 'foobar' };
let arr = [3, o, 4, 5];

arr.find(x => console.log(this), o);

The lambda is capturing this from the current scope, and so your code logs window four times. It works as expected if you convert the lambda to a regular anonymous function. Your callback doesn't return a truthy value though, so it won't ever find anything. — user47589
– user47589, Commented Nov 20, 2018 at 21:01
What do you expect this to refer to? From what you posted it's not clear why exactly it's undefined, but it would not be weird for it to be undefined. — Pointy
– Pointy, Commented Nov 20, 2018 at 21:01
arr.find receives a condition and returns the first element that satisfies the condition. What you're doing is "out of the given array, return the first element that - console.log". console.log returns undefined, so the condition returns undefined for all elements and eventually finds nothing. — Gilad Bar
– Gilad Bar, Commented Nov 20, 2018 at 21:03
Thanks for the explanation @Amy. Im new to JS and did not think of this mechanims. — Pascal K
– Pascal K, Commented Nov 20, 2018 at 21:16

Mark · Accepted Answer · 2018-11-20 21:12:21Z

4

If you want to use the second parameter of find() to set this you need to pass a regular function because you can't re-bind this to arrow functions:

let o = { name: 'foobar' };
let arr = [3, o, 4, 5];

let p = arr.find(function(x){
         console.log(this)
         return x === this
 }, o);

 console.log("found:", p)

edited Nov 20, 2018 at 21:12

answered Nov 20, 2018 at 21:04

Mark

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1 Comment

Mark Over a year ago

What I'm saying @geoge is that you can't do call bind(someObj) on an arrow function to set the value of this find()'s second param is a value to rebind the function to. Maybe I phrased it poorly.

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