4.Type Any

Type: any

You could ask — what if I don't know what kind of value my variable will have?

1. Let's flush our function code and type ine the following:

  let myVar;
 
   myVar = 1;      //number
   myVar = true;   //boolean
   myVar = 'mdb';  //string
 

The TypeScript compiler doesn't complain. Why!?

2. Hover over the myVar declaration, what do you see?


TypeScript allows you to use a special type any. It allows you to use dynamic typing but importantly — it requires you to use it consciously.

3. What is actually type of the variable myVar? Let's check it:

  myVar = 1;     //number
   console.log(typeof(myVar));
   myVar = true;  //boolean
   console.log(typeof(myVar));
   myVar = 'mdb'; //string
   console.log(typeof(myVar));
 

The output:


4. Now let's add an explicit type, cast after the var declaration:

  let myVar: number;

Immediately, the compiler will show two errors regarding the second, and third assignments

Other types:

We used already four different types of variables (number, string, boolean and any). Are there any others? Yes, there are.

  let a: number;                    //numeric type
   let b: string;                    //string
   let c: boolean;                   //true or false
   let d: any;                       //any (dynamic)
   let e: number[] = [1,2,3];        //array of numbers
   let f: string[] = ['a','b','c'];  //array of strings
   let g: any[] = [true, 1, 'a'];    //array of any
   

As you can see, except for basic types which we already covered you can also create arrays of different types including the any type. There is also one more type of variable — enum but we will cover it in the future.