How the amend function works

The amend function is a little helper function. It is defined as:

function amend<O1, O2>(o1: O1, o2: O2) {
    return assign({}, o1, o2);
}

And assign is just a substitute for the gradually appearing standard function Object.assign.

The purpose of amend is to fill in for the object spread operator that is not yet in TypeScript. It would be cool if we could say:

{ ...book, title }

which would mean: make a new object with all the properties of book, and add (or replace) the title property with the value of the title variable. But in the meantime this isn't so bad:

amend(book, { title })