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TypeScript code kata list

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005 TypeScript - var let const

Duration

10 minutes

Brief

Working with var, let, and const and their scopes.

For more information

BING/GOOGLE: “TypeScript var let const”

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/005%20TypeScript%20-%20var%20let%20const/before
• After
  
  • https://github.com/robertdunaway/katas-typescript/tree/master/005%20TypeScript%20-%20var%20let%20const/after

Kata

Create a few variables with “var”, “let”, and “const”.

    var myVar: number = 111;
    let myLet: number = 222;
    const myConst: number = 333;

Demonstrate what happens when declaring a variable with “var” in the root and then again inside a block statement like foreach or if(true).
Here is one possible example:

    if (true) {
        var myVar: number = 444;
    }
    console.log('myVar = ' + myVar);

Demonstrate what happens when doing the same with a variable declared with “let”.

    if (true) {
        let myLet: number = 555;
    }
    console.log('myLet = ' + myLet);

Try changing the value of the constant you created earlier. You will receive error message, at design time, explaining why you can’t change the value.

    myConst = 123;

Maybe you think you can just ignore this message and fall back on the Gulp task to transpile this errant TypeScript code.

You’d be wrong…

Next

Take a few minutes and imagine more examples.