Deep copy an array in Angular 2 + TypeScript

Question

I have an array of objects that is an input. Lets call it content.

When trying to deep copy it, it still has a reference to the previous array.

Answer 1

I found deep copy method in angular devkit, It's very normal, so... maybe you can just implement yourself or use that.

I prefer to use loadash, there a lot of objects and array operation methods that can use.

import { deepCopy } from '@angular-devkit/core/src/utils/object';

export class AppComponent {
  source = {
    ....
  }
  constructor() {
     const newObject = deepCopy(this.source);
  }
}

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.1000.8
@angular-devkit/build-angular     0.1000.8
@angular-devkit/build-optimizer   0.1000.8
@angular-devkit/build-webpack     0.1000.8
@angular-devkit/core              10.0.8
@angular-devkit/schematics        10.0.8
@angular/cli                      10.0.8
@ngtools/webpack                  10.0.8
@schematics/angular               10.0.8
@schematics/update                0.1000.8
rxjs                              6.5.5
typescript                        3.9.7
webpack                           4.43.0

Answer 2

Alternatively, you can use the GitHub project ts-deepcopy, which is also available on npm, to clone your object, or just include the code snippet below.

/**
 * Deep copy function for TypeScript.
 * @param T Generic type of target/copied value.
 * @param target Target value to be copied.
 * @see Source project, ts-deepcopy https://github.com/ykdr2017/ts-deepcopy
 * @see Code pen https://codepen.io/erikvullings/pen/ejyBYg
 */
export const deepCopy = <T>(target: T): T => {
  if (target === null) {
    return target;
  }
  if (target instanceof Date) {
    return new Date(target.getTime()) as any;
  }
  if (target instanceof Array) {
    const cp = [] as any[];
    (target as any[]).forEach((v) => { cp.push(v); });
    return cp.map((n: any) => deepCopy<any>(n)) as any;
  }
  if (typeof target === 'object' && target !== {}) {
    const cp = { ...(target as { [key: string]: any }) } as { [key: string]: any };
    Object.keys(cp).forEach(k => {
      cp[k] = deepCopy<any>(cp[k]);
    });
    return cp as T;
  }
  return target;
};

Answer 3

This is working for me:

this.listCopy = Object.assign([], this.list);

Answer 4

A clean way of deep copying objects having nested objects inside is by using lodash's cloneDeep method.

For Angular, you can do it like this:

Install lodash with yarn add lodash or npm install lodash.

In your component, import cloneDeep and use it:

import * as cloneDeep from 'lodash/cloneDeep';
...
clonedObject = cloneDeep(originalObject);

It's only 18kb added to your build, well worth for the benefits.

I've also written an article here, if you need more insight on why using lodash's cloneDeep.