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

To use the mapObject function from the Underscore library in TypeScript, make sure to have the library installed and imported at the top of your TypeScript file:

index.ts
import * as _ from 'underscore';
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Next, call the mapObject function on an object you wish to map values for. mapObject is a generic function that returns an object of the same shape as the input object, with values mapped by the provided function. Note that the callback function receives two arguments: the current value and the corresponding key.

Here's an example of using the mapObject function in TypeScript:

index.ts
interface User {
  id: number;
  firstName: string;
  lastName: string;
}

const user1: User = { id: 1, firstName: 'John', lastName: 'Smith' };
const user2: User = { id: 2, firstName: 'Jane', lastName: 'Doe' };
const usersById: Record<number, User> = { 1: user1, 2: user2 };

const usersByName: Record<string, User> = _.mapObject(
  usersById,
  (user) => `${user.firstName} ${user.lastName}`
);

console.log(usersByName);
// Output: { '1': 'John Smith', '2': 'Jane Doe' }
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In this example, we have an object usersById with user data for two users. We then use mapObject with a callback function that concatenates the first and last names of each user, mapping them to new keys in a new object usersByName.

Note that the output object usersByName has string keys instead of numeric keys, since the callback function generates new keys based on the mapped values. If you need to preserve the numeric keys from the original object, you'll need to use a different approach or write a custom mapping function.