How can I preserve lexical scope in TypeScript with a callback function

Question

I have a TypeScript class, with a function that I intend to use as a callback:

removeRow(_this:MyClass): void {
    ...
    // \'this\' is now the window obj         


        

Answer 1

Building upon sly and Zac's answers with types: A complete hello world example. I hope this is welcome, seeing as this is the top result in Google, when searching for "typescript javascript callbacks"

type MyCallback = () => string;

class HelloWorld {

    // The callback
    public callback: MyCallback = () => {
        return 'world';
    }

    // The caller
    public caller(callback: MyCallback) {
        alert('Hello ' + callback());
    }
}

let hello = new HelloWorld();
hello.caller(hello.callback);

This gets transpiled into:

var HelloWorld = (function () {
    function HelloWorld() {
        // The callback
        this.callback = function () {
            return 'world';
        };
    }
    // The caller
    HelloWorld.prototype.caller = function (callback) {
        alert('Hello ' + callback());
    };
    return HelloWorld;
}());
var hello = new HelloWorld();
hello.caller(hello.callback);

Hope someone finds it just a little useful. :)