Union types are used when a value can be more than a single type.
Such as when a property would be string or number .
Union | (OR)
Using the | we are saying our parameter is a string or number :
Example
function printStatusCode(code: string | number) {
console.log(`My status code is ${code}.`)
}
printStatusCode(404);
printStatusCode('404');Union Type Errors
Note
you need to know what your type is when union types are being used to avoid type errors:
Example
function printStatusCode(code: string | number) {
console.log(`My status code is ${code.toUpperCase()}.`) // error: Property 'toUpperCase' does not exist on type 'string | number'. Property 'toUpperCase' does not exist on type 'number'
}