CODEWITHSUNDEEP
javascriptfunctional-programming
Qbik
Qbik

Reputation: 6147

JS using partially parametrized function

I'm very new to JS, I've tried code below :

function isBigEnough(element, index, array, threshold) {
  return (element >= threshold);
}
[1, 2, 3].every(isBigEnough(threshold=0)

I thought it doesn't work because prototype (in Array.prototype.filter()) does not contain threshold, so it is types mismatch, but we can't define like this : isBiggerThenZero = isBigEnough(threshold=0) so is there nice workaround for this case ?

Upvotes: 0

Views: 68

Answers (2)

deathangel908
deathangel908

Reputation: 9699

When you do [1, 2, 3].every(isBigEnough(0)). It:

  • Calls isBigEnough that returns false.
  • Executes [1, 2, 3].every(false). Where false is not a function. SO it gives you an error.

You can use a closure that binds threshold value to the returned function:

function isBigEnough(threshold) {
  return function(element, index, array) {
     return (element >= threshold);
  }
}
[1, 2, 3].every(isBigEnough(0))

Upvotes: 4

Jonas Wilms
Jonas Wilms

Reputation: 138257

Default parameters must be in the function declaration, e.g:

function isBigEnough(element, index, array, threshold=0) {
  return (element >= threshold);
}
[1, 2, 3].every(isBigEnough);

However, now its difficult to pass threshold:

[1,2,3].every((...a)=>isBigEnough(...a,2));

So you could rather do:

function isBigEnough(threshold=0,element, index, array) {
 return (element >= threshold);
}
[1, 2, 3].every(isBigEnough.bind(null,5));//threshold=5

Upvotes: 1

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