How to get length of previous array in chain function

Question

Try to do something with array with unpredictable result, something like return random member of filtered array

let tempArr = [1,2,3,4,5].filter(x=>x>2);
return tempArr[Math.floor(Math.random()*tempArr.length)];  // 3, 4 or 5

Just want to make it more clear by using chain function, but the following code is not working, this.length is always 1

return [1,2,3,4,5]
         .filter(x=>x>2)
         .at(Math.floor(Math.random()*this.length)); // always returns `3`

What's the correct way to do this?

You don't. You'll need a variable to refer to the array twice. Chaining doesn't make it "more clear" anyway. — Bergi
– Bergi, Commented Oct 3, 2022 at 3:44
this.length is always 1 because this is not what you think it is — Jaromanda X
– Jaromanda X, Commented Oct 3, 2022 at 3:54

A1exandr Belan · Accepted Answer · 2022-10-03 05:12:35Z

2

I doubt you can achieve that flow with vanila js, but if you use something like the lodash library, you can make the chain and make code more readable.

const result = _([1,2,3,4,5])
  .filter(x => x > 2)
  .sample();
  
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0 }

<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>

answered Oct 3, 2022 at 5:12

A1exandr Belan

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2 Comments

Byzod Over a year ago

That's what I want, clear and easy to read

Byzod Over a year ago

I did this by extending Array.prototype.sample, I know I shouldn't extend base object, but since this is a greasemonkey script running in sandbox and the only user is myself, I think it's fine :)

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