how to use the isnan function from the underscore library in typescript

To use the isNaN function from the Underscore library in TypeScript, first you need to install the library itself. You can do so by running the following command:

npm install underscore
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Next, you need to include the type declaration file for Underscore in your TypeScript project. If you're using a module-based system (such as ES6 modules), you can import the type declaration like this:

index.ts
import * as _ from 'underscore';

// use isNaN function
const result: boolean = _.isNaN(NaN);
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If you're not using a module-based system, you can use a triple-slash directive to reference the type declaration file in your TypeScript code:

index.ts
/// <reference path="./node_modules/underscore/underscore.d.ts" />

// use isNaN function
const result: boolean = _.isNaN(NaN);
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Then, you can use the isNaN function from the Underscore library like any other function by passing it a value and getting a boolean as a result.

index.ts
const result: boolean = _.isNaN(NaN);

console.log(result) // true
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The isNaN function is used to determine whether a value is NaN (not a number) or not. If the value is not a number, the function will return true. Otherwise, it will return false.