How to copy matching properties from one object to another

Question

I have these two objects:

obj1 = {a: '', b: ''}
obj2 = {a: '1', b: '2', c: '3'}

I want to copy all matching properties from obj2 to obj1. What is the best way of doing that in Typescript?

Answer 1

what is the best way of doing that in typescript

Same as in JavaScript. Just use Object.keys

The following code moves stuff from obj2 to obj1:

let obj1 = {a: '', b: ''}
let obj2 = {a: '1', b: '2', c: '3'}

Object.keys(obj2).forEach(key=>obj1[key]=obj2[key]);

For any condition like must not already be in obj1 etc you can do that check in the forEach

Answer 2

If you don't mind any keys of obj2 not exist in obj1, a clearer way is using Object.assign(obj1, obj2):

Answer 3

I think @basarat meant to iterate over the target properties not the source ones like this

function CopyMatchingKeyValues(Target, Source) {
    return Object.keys(Target).forEach(key => {
        if (Source[key] !== undefined)
            Target[key] = Source[key];
    });
}

Actually he is testing for key matching it won't matter.

• For performance we probably want to pick the shortest list of the keys.