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

To use the chain function from the underscore library in TypeScript, you need to install the corresponding type definition files for underscore. The most common package to use is @types/underscore.

To install it using npm, run the following command in your terminal:

npm install @types/underscore
30 chars
2 lines

Once you have that installed, you can import underscore and use the chain function like this:

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

const numbers = [1, 2, 3, 4, 5];

const result = _.chain(numbers)
  .filter(num => num % 2 === 0)
  .map(num => num * 2)
  .value();

console.log(result); // [4, 8]
199 chars
11 lines

In this example, the chain function takes an array of numbers, and then applies a series of functions to it using method chaining.

The filter function returns only the even numbers from the array, and the map function doubles each of those even numbers. Finally, the value function returns the final result of the method chain as an array.

The result variable will contain the final output of the method chain: an array of [4, 8].