Union is a way in typescript to define a variable that can hold multiple types of values. For example, we can create a variable that can hold both string and int type. In this post, we will learn how to use union type in typescript with example.
Pipe symbol (|) is used for union type. Below is the syntax of union type:
let varName: type1 | type2
Let’s take a look at the below example:
let myVariable : string | boolean; myVariable = 'Hello'; myVariable = true; myVariable = 20;
In this example, we created one variable myVariable of type string | boolean. We are assigning three different types of data to this variable.
In the last line, we are assigning one number to this variable myVariable. It will throw one compile-time error:
type '20' is not assignable to type 'string | boolean'
There is no limit of types we can add to union type. For example, if we add number as another type, this error will be removed:
let myVariable : string | boolean | number; myVariable = 'Hello'; myVariable = true; myVariable = 20;