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?
7 Answers
"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.)
Utilize toString() or toLocaleString(), for example:
var page_number:number = 3;
window.location.hash = page_number.toLocaleString();
These throw an error if page_number is null or undefined. If you don't want that you can choose the fix appropriate for your situation:
// Fix 1:
window.location.hash = (page_number || 1).toLocaleString();
// Fix 2a:
window.location.hash = !page_number ? "1" page_number.toLocaleString();
// Fix 2b (allows page_number to be zero):
window.location.hash = (page_number !== 0 && !page_number) ? "1" page_number.toLocaleString();
One can also use the following syntax in typescript. Note the backtick " ` "
window.location.hash = `${page_number}`
window.location.hash is a string, so do this:
var page_number: number = 3;
window.location.hash = String(page_number);
This is some short ways
any_type = "" + any_type;
any_type = String(any_type);
any_type = `${any_type}`;
const page_number = 3;
window.location.hash = page_number as string; // Error
"Conversion of type 'number' to type 'string' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first." -> You will get this error if you try to typecast number to string. So, first convert it to unknown and then to string.
window.location.hash = (page_number as unknown) as string; // Correct way
Just use: page_number?.toString()
