Which is the the best way (if there is one) to cast from number to string in Typescript?
var page_number:number = 3;
window.location.hash = page_number;
In this case the compiler throws the error:
Type 'number' is not assignable to type 'string'
Because location.hash
is a string.
window.location.hash = ""+page_number; //casting using "" literal
window.location.hash = String(number); //casting creating using the String() function
So which method is better?
"Casting" is different than conversion. In this case, window.location.hash
will auto-convert a number to a string. But to avoid a TypeScript compile error, you can do the string conversion yourself:
window.location.hash = ""+page_number;
window.location.hash = String(page_number);
These conversions are ideal if you don't want an error to be thrown when page_number
is null
or undefined
. Whereas page_number.toString()
and page_number.toLocaleString()
will throw when page_number
is null
or undefined
.
When you only need to cast, not convert, this is how to cast to a string in TypeScript:
window.location.hash = <string>page_number;
// or
window.location.hash = page_number as string;
The <string>
or as string
cast annotations tell the TypeScript compiler to treat page_number
as a string at compile time; it doesn't convert at run time.
However, the compiler will complain that you can't assign a number to a string. You would have to first cast to <any>
, then to <string>
:
window.location.hash = <string><any>page_number;
// or
window.location.hash = page_number as any as string;
So it's easier to just convert, which handles the type at run time and compile time:
window.location.hash = String(page_number);
(Thanks to @RuslanPolutsygan for catching the string-number casting issue.)