Learn React with TypeScript 3

String literal types

A variable of a string literal type can only be assigned the exact string value specified in the string literal type.

In the TypeScript playground, let's go through an example:

1. Let's create a string literal type called Control that can only be set to the "Textbox" string:

type Control = "Textbox";

2. Let's now create a variable called notes with our Control type and set this to "Textbox":

let notes: Control;notes = "Textbox";

As we would expect, the TypeScript compiler is happy with this.

3. Now let's set our variable to a different value:

notes = "DropDown";

We get the compilation error Type '"DropDown"' is not assignable to type '"Textbox"':

4. As with all other types in TypeScript, null and undefined are valid values ...