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

To use the indexOf function from the Underscore library in TypeScript, you can follow these steps:

1. Install the Underscore library using npm:

   index.ts
   npm install underscore
   23 chars
   2 lines

2. In your TypeScript file, import the Underscore library:

   index.ts
   import * as _ from 'underscore';
   33 chars
   2 lines

3. Now, you can use the indexOf function from the Underscore library to find the index of an element in an array:

   index.ts
   const numbers = [1, 2, 3, 4, 5];
   
   console.log(_.indexOf(numbers, 3)); // Output: 2
   83 chars
   4 lines

   In this example, the indexOf function returns the index of the element 3 in the numbers array, which is 2.

4. If you want to use the indexOf function in a TypeScript project without installing the Underscore library, you can declare the function type like this:

   index.ts
   declare function indexOf<T>(array: T[], value?: T, isSorted?: boolean): number;
   80 chars
   2 lines

   This declaration tells TypeScript that the indexOf function can accept an array of any type T, an optional value parameter of type T, and an optional isSorted parameter of type boolean, and it returns a number value.

   Now, you can use the indexOf function in your TypeScript project without importing the Underscore library:

   index.ts
   const numbers = [1, 2, 3, 4, 5];
   
   console.log(indexOf(numbers, 3)); // Output: 2
   81 chars
   4 lines