What does the pipe, | mean in TypeScript?

In TypeScript, the pipe symbol | is used to denote a union type, which is a way of declaring that a variable or parameter can hold a value of different types. The union type is essentially a way to say that a value can be one of several types, and it is represented by listing those types separated by the pipe symbol.

For example, if you have a variable that can hold either a number or a string, you would declare it as number | string. This tells TypeScript that the variable is allowed to hold a value of either type. Here's a practical example:

let value: number | string;
value = 42; // OK
value = "hello"; // OK
value = false; // Error: Type 'boolean' is not assignable to type 'number | string'.

In this example, assigning a number or a string to value is perfectly fine, but trying to assign a boolean results in a type error because boolean is not pa...