What is Type Narrowing in TypeScript ?
Last Updated :
23 Feb, 2024
Type narrowing is a process of refining or narrowing down the type using certain conditions with a particular code block. It will help developers as well as TypeScript itself to infer the more accurate types within the code and work with them in a clean and strict code environment. The type narrowing can be done using the type guards(typeof, instanceof operator), equality operators(==, ===), etc.
Syntax:
typeof variable === another comparing type;
Example: The below code will explain the use of the typeof operator to narrow the type in TypeScript.
Javascript
function typeNarrowing(arg: any): boolean {
return typeof arg === 'number' ;
}
typeNarrowing(20099) ?
console.log( "Type is narrowed to number" ) :
console.log( "Type can not be narrowed to number" );
typeNarrowing( "GeeksforGeeks" ) ?
console.log( "Type is narrowed to number" ) :
console.log( "Type can not be narrowed to number" );
|
Output:
Type is narrowed to number
Type can not be narrowed to number
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