Deep copy or clone in TypeScript

deep-copy.ts

/**
 * 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;
};

I faced an issue when cloning object which had empty objects inside - the empty objects were only passed by reference and therefore any change to the new object affected the old one. I removed the 'target !== {}' to make it work for me. @erikvullings was there any other reason except from optimization for having the condition there?

This working with array, objects and persist datatype

function deepCopyObj<T>(obj: T): T { return JSON.parse(JSON.stringify(obj)) as T; }

True, but it is a rather expensive operation, and it will fail on circular objects, i.e. objects referring to itself.

I faced an issue when cloning object which had empty objects inside - the empty objects were only passed by reference and therefore any change to the new object affected the old one. I removed the 'target !== {}' to make it work for me. @erikvullings was there any other reason except from optimization for having the condition there?

No, not really - this copy/clone function is for basic usage only. I've also ported it to a more elaborate version that takes care of several other issues too, deep-copy-ts. Or you can get it from npm.