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

To use the compose function from the Underscore library in TypeScript, first, you need to install the Underscore library. You can install it via npm.

index.ts
npm install underscore
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After installing the library, you need to import it in your TypeScript file.

index.ts
import * as _ from 'underscore';
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Then, you can use the _.compose function to combine multiple functions into a single function. Here is an example TypeScript code snippet that demonstrates how to use the _.compose function.

index.ts
interface User {
  name: string;
  age: number;
  email: string;
}

const users: User[] = [
  { name: 'Alice', age: 25, email: 'alice@example.com' },
  { name: 'Bob', age: 30, email: 'bob@example.com' },
  { name: 'Charlie', age: 35, email: 'charlie@example.com' },
];

const filterAgeAbove30 = (users: User[]) => _.filter(users, user => user.age > 30);
const mapEmails = (users: User[]) => _.map(users, user => user.email);
const joinEmails = (emails: string[]) => emails.join(', ');

const getEmailsOfUsersAbove30 = _.compose(joinEmails, mapEmails, filterAgeAbove30);
const emailsOfUsersAbove30 = getEmailsOfUsersAbove30(users);
console.log(emailsOfUsersAbove30); // Output: "bob@example.com, charlie@example.com"
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In this code snippet, we define three functions: filterAgeAbove30, mapEmails, and joinEmails. filterAgeAbove30 filters the users who are above 30 years old. mapEmails maps the users to their emails. joinEmails joins multiple emails into a single string separated by a comma.

Then, we use the _.compose function to compose these three functions into a single function called getEmailsOfUsersAbove30. Finally, we apply the getEmailsOfUsersAbove30 function to the users array to get the emails of the users who are above 30 years old.