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About Typescript

tip

Typescript is exactly the same as Javascript, with optional types on top of it.

How do you use types in Typescript?​

You can (optionally) specify a type after a variable, by using a colon: const x: number.

It is very useful to specify the types expected by a function:

function doSomething(x: number, y: number, title: string): number {
    // . . .
}

The above function takes two numbers and a string, and returns a number.

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Having precise type definitions allows your IDE to give you much better errors and warnings, and it makes your life a lot easier!

If you still want the possibility for a variable to have multiple types, you can use a union: 

const x: number | string

If you want optional arguments, declare them with a ?:

function doSomething(x: number, y: number, title?: string): number {
    // . . .
}

Here title is an optional parameter.

Going further

Typescript has many more nice features: enums, better classes, objects with well-defined fields (called interface) etc.

Check out the Typescript Handbook if you want to know more.

How do you use Javascript?​

We won't need much knowledge of Javascript for this class.

The only thing I want you to remember is the proper way of declaring variables:

tip

Use const, or let.

const x = 10

A variable declared with const cannot be changed afterwards. It is a good practice to use const when your variable doesn't change, because it makes it clearer to the reader (and to yourself) that you don't intend to change this variable for the moment.

let x = 10

If you need a mutable variable, then it is perfectly fine to declare it with let. I would recommend to always start with a const variable, and then change it to let once you decide to make it vary in your program.

And please, forget var. It is the old way of declaring variables and it can have confusing behaviour, so we introduced const and let in the language to replace var. Never ever use var again.

Good to know

In Javascript the semicolons at the end of every line are not required. It is only a stylistic choice and I'll let you decide which convention you prefer.