CODEWITHSUNDEEP
javascriptunderscore.js
chopper draw lion4
chopper draw lion4

Reputation: 13487

_.memoize only cache's first argument

I realized today that the _memoize function only caches results for the first argument provided.

function add(a, b) {
  return a + b;
}
var sum = _.memoize(add);
console.log(sum(1,2));
>>> 3
console.log(sum(1,5));
>>> 3

Is this a bug or deliberate?

Upvotes: 2

Views: 1972

Answers (2)

Raks Paul
Raks Paul

Reputation: 1

const g = _.memoize(([a, b]) => a + b)
console.log(g([1, 2]))
console.log(g([1, 3]))
console.log(g([1, 4]))

pass all as the first argument

Upvotes: 0

Amadan
Amadan

Reputation: 198314

Deliberate. Relevant docs:

The default hashFunction just uses the first argument to the memoized function as the key.

But good news is you can change this behaviour by introducing your own hash function.

function myInefficientHashFunction() {
  // not really an efficient hash function
  return JSON.stringify(arguments);
}

function add(a, b) {
  return a + b;
}
var sum = _.memoize(add, myInefficientHashFunction);

document.getElementById('one_two').textContent = sum(1, 2)
document.getElementById('one_three').textContent = sum(1, 3)
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.7.0/underscore-min.js"></script>
<div>1 + 2 = <span id="one_two"/></div>
<div>1 + 3 = <span id="one_three"/></div>

Upvotes: 9

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