TypeScript definition for function that merges two objects

Question

Given a function that takes in two objects of different types, object A and object B, merges both objects into one and returns that merged object:

/**  
 * @description Merge the contents of two objects into a single object
 * @param {Object} target The target object of the merge
 * @param {Object} ex The object that is merged with target
 * @return {Object} The target object
 * @example
 * var A = {a: function() {console.log(this.a}};
 * var B = {b: function() {console.log(this.b}};
 *
 * pc.extend(A,B);
 * A.a();
 * // logs "a"
 * A.b();
 * // logs "b"
 */

This is what i came up with but somehow I'm not sure this is right:

function extend<T>(target: T, ex: T): T

What should the function declaration look like? Should I be using generic types for this? How do I define the merged type being returned?

Jeff Mercado · Accepted Answer · 2017-12-11 16:53:53Z

3

You're describing an Intersection Type, a combination of multiple types. Your scenario is even explained in the documentation.

In your case, you'll need to introduce a second generic parameter, to represent the other type. Your signature should look like this:

function extend<T, U>(target: T, ex: U): T & U

answered Dec 11, 2017 at 16:53

Jeff Mercado

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1 Comment

snowfrogdev Over a year ago

Thanks, I feel kind of dumb. I had looked at the 'mixins' and 'declaration merging' part of the documentation. Thanks for pointing me in the right direction. I'm sure this question and your answer will still be useful for other TypeScript newbies like me.

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