How can I add a property calculated by a JavaScript extension with C#?

Question

I have array and want access by property (not function) like:

let arr = [1,2,3];
console.log("last element: ", arr.last)

I try like it, but got error:

Array.prototype.last = (() => {
    return this[this.length - 1];
})();

Update 1: yes i know how do it like extend method:

 Array.prototype.mysort = function() {
        this.sort(() => Math.random() - 0.5);
        return this;
    }
    myarray.mysort();

but how do it like property?

myarray.mysort;

Don't use an arrow function if you want to use `this`. Use a traditional function. — Barmar, Mar 23 '22 at 15:20
@Barmar because i come from C# and cant find how in js prototype like property (not call like function) — padavan, Mar 23 '22 at 15:26
Also remove the `()` at the end. That calls the function immediately, instead of storing the function. — Barmar, Mar 23 '22 at 15:28
if i change to function() i will call extension like method . Questiong about how call like property. Okay I'll take a look about getters — padavan, Mar 23 '22 at 15:30
I attempted to make sense of your post title and format it as a proper sentence. Please revise further if necessary. — isherwood, Mar 23 '22 at 15:40

score 1 · Accepted Answer · answered Mar 23 '22 at 15:35

You can do this with a getter. You need to use Object.defineProperty() to add a getter to an existing object, in this case the Array.prototype object.

Object.defineProperty(Array.prototype, "last", {
  get: function() {
    return this[this.length - 1];
  }
});

const a = [1, 2, 3];
console.log(a.last);

How can I add a property calculated by a JavaScript extension with C#?

1 Answers1