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?
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Answer
“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.)