Signal-Desktop/ts/util/assignWithNoUnnecessaryAllo...

31 lines
938 B
TypeScript

// Copyright 2020-2022 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
import { has } from 'lodash';
/**
* This function is like `Object.assign` but won't create a new object if we don't need
* to. This is purely a performance optimization.
*
* This is useful in places where we don't want to create a new object unnecessarily,
* like in reducers where we might cause an unnecessary re-render.
*
* See the tests for the specifics of how this works.
*/
export function assignWithNoUnnecessaryAllocation<T extends object>(
obj: Readonly<T>,
source: Readonly<Partial<T>>
): T {
// We want to bail early so we use `for .. in` instead of `Object.keys` or similar.
// eslint-disable-next-line no-restricted-syntax
for (const key in source) {
if (!has(source, key)) {
continue;
}
if (!(key in obj) || obj[key] !== source[key]) {
return { ...obj, ...source };
}
}
return obj;
}