Literal Type

works similarly to enums in Java.

you can specify a type and a specific value at once, as shown below.

literal type
let dir:"LEFT";

• string type, only accepting the value "LEFT"

only the string "LEFT" can be bound to this variable.

literal type
let dir:"LEFT";

dir = "left"; // #ERROR
dir = "Left"; // #ERROR

dir = "LEFT"; // #SUCCESS

rather than being used alone, this odd type is used to function like an enum in Java, with the shape

when Java only accepts one of three values, it looks like this

JAVA
public enum Dir {
  LEFT,
  CENTER,
  RIGHT
}

in Typescript, this would look like this

JAVASCRIPT
let dir = "LEFT"|"CENTER"|"RIGHT";

• only three strings are allowed in the variable dir

alternatively, you can declare it as a separate type.

JAVASCRIPT
type Dir = "LEFT"|"CENTER"|"RIGHT"; // declare separate type

let where:Dir; // restricted to the type Dir

• the variable where can only contain one of the strings "LEFT", "CENTER", or "RIGHT"