The Object.assign() method copies all enumerable own properties from one or more source objects to a target object and returns the modified target object.

Spread syntax (...) allows an object expression to be expanded in places where zero or more key-value pairs are expected.

(c) MDN

🐊Putout plugin adds ability to convert Object.assign() to merge spread since it shorter but does (mostly) the same.

npm i @putout/plugin-convert-object-assign-to-merge-spread -D

{
    "rules": {
        "convert-object-assign-to-merge-spread": "on"
    }
}

function merge(a) {
    return Object.assign({}, a, {
        hello: 'world',
    });
}

function merge(a) {
    return {
        ...a,
        hello: 'world',
    };
}

MIT