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Union types are used when a value can be more than a single type
Using the |
we are saying our parameter is a string
or number
:
function printStatusCode(code: string | number) {
console.log(`My status code is ${code}.`)
}
printStatusCode(404);
printStatusCode('404');
function printStatusCode(code: string | number) {
console.log(`My status code is ${code.toUpperCase()}.`) // error: Property 'toUpperCase' does not exist ontype 'string | number'.
Property 'toUpperCase' does not exist on type 'number'
}
In our example we are having an issue invoking toUpperCase()
as its a
string
method and number
doesn't have access
to it.