Function

isConst public

Module: @glimmer/tracking/primitives/cache

Defined in packages/@ember/-internals/metal/lib/cache.ts:78 

import { isConst } from '@glimmer/tracking/primitives/cache';

Can be used to check if a memoized function is constant. If no tracked state was used while running a memoized function, it will never rerun, because nothing can invalidate its result. isConst can be used to determine if a memoized function is constant or not, in order to optimize code surrounding that function.

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import { tracked } from '@glimmer/tracking';
import { createCache, getValue, isConst } from '@glimmer/tracking/primitives/cache';

class State {
  @tracked value;
}

let state = new State();
let computeCount = 0;

let counter = createCache(() => {
  // consume the state
  state.value;

  return computeCount++;
});

let constCounter = createCache(() => {
  return computeCount++;
});

getValue(counter);
getValue(constCounter);

isConst(counter); // false
isConst(constCounter); // true

If called on a cache that hasn't been accessed yet, it will throw an error. This is because there's no way to know if the function will be constant or not yet, and so this helps prevent missing an optimization opportunity on accident.