http://robertdunaway.github.io

TypeScript code kata list

All code kata lists

021 TypeScript - callbacks

Duration

10 minutes

Brief

Functions can be passed into other functions and returned from functions. Passing functions into another function is a call back.

For more information

BING/GOOGLE: “TypeScript callbacks”

Instructions

Get tutorial folder or the entire katas-typescript repo.
Open the [before/*.sln] file and execute the kata.
Feel free to execute this kata multiple times because repetition creates motor memory.

Github

• Before (start kata with this)
  
  • https://github.com/robertdunaway/katas-typescript/tree/master/021%20TypeScript%20-%20callbacks/before
• After
  
  • https://github.com/robertdunaway/katas-typescript/tree/master/021%20TypeScript%20-%20callbacks/after

Kata

Create a simple function that you can use as a callback function that only outputs some short text message to the console.

Create a function that accepts a function as a callback and then calls the callback function.

Now call your new function and pass in your simple output function.

    // create a function to be used as a callback.  This is our callback function.
    var myCB = function () {
        console.log('The callback just ran...');
    };

    // create a function and pass in the callback method.
    function myFunction(cb: () => void) {
        cb();
    }

    myFunction(myCB); // calling the new function and pass in the callback.

Now create a new function, used as a callback, that accepts a value that will be outputted to the console log.

Create a function that receives the callback as a parameter and calls the callback. This function should accept a callback function and two numbers that will be added together and sent to the callback.

    // create another callback function whose job is to output whatever it's 
    // passed back to display.  If nothing is passed back then output a default value.
    var myConsoleLog = function (output: string = 'Nothing was passed back to output') {
        console.log(output);
    }

    // create a function and pass in the callback method.
    function add(cb: (string) => void, a: number, b: number) {
        var c = a + b;
        cb('a + b = ' + c);
    }

    // call the new add function and pass in the callback function and two numbers.
    add(myConsoleLog, 2, 3);

Next

Take a few minutes and imagine more examples.