Array, Tuple, Union in TypeScript
Array use of variables to store values. Array types can be written in one of two ways. In the first, you use the type of the elements followed by  to denote an array of that element type.
Declaring and Initializing Arrays
To declare an initialize an array in Typescript uses the following syntax:
let arrayName:datatype //declaration
many way array declaration
We know that an array holds multiple values of the same datatype. But sometimes, we may need to store a collection of values of different data types in a single variable. Arrays will not provide this feature, but TypeScript has datatype called tuple to achieve this purpose.
We may want to represent a value as a pair of a string and a number:
Declare a tuple type
Initialize it incorrectly
Accessing an element outside the set of known indices fails with an error:
Destructuring a Tuple
we can define a variable that can have multiple types of values. Two or more data types are combined using the pipe symbol (|) to denote a Union Type. In other words, a union type is written as a sequence of types separated by vertical bars.
Example: Union Type Variable
Reference: https://www.typescriptlang.org/docs/handbook/basic-types.html https://www.javatpoint.com/