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getOrInsertComputed

Returns a map entry or stores a computed value when missing

since v12.7.0

Usage

Computes and stores a value only when the key has no entry yet.

import * as _ from 'radashi'

const counts = new Map<string, number>()

_.getOrInsertComputed(counts, 'clicks', () => 1) // => 1
_.getOrInsertComputed(counts, 'clicks', () => 5) // => 1

This function is most useful when the computed value is expensive to compute, e.g. a complex object or a non-trivial math calculation.

You can use a WeakMap instead, if you’d like to associate the computed value with an object reference.

import * as _ from 'radashi'

const values = new WeakMap<object, { count: number }>()
const key = {}
_.getOrInsertComputed(values, key, () => ({ count: 1 })) // => { count: 1 }
_.getOrInsertComputed(values, key, () => ({ count: 2 })) // => { count: 1 }

Inspired by TC39’s Upsert proposal.