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

To use the partition function from the underscore library in typescript, first you need to install the underscore library:

index.ts
npm install underscore
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Then, you can import the partition function from underscore and use it as follows:

index.ts
import { partition } from 'underscore';

const arr: number[] = [1, 2, 3, 4, 5];
const [even, odd] = partition(arr, (num: number) => num % 2 === 0);

console.log(even); // [2, 4]
console.log(odd); // [1, 3, 5]
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The partition function takes two arguments: the array to be partitioned, and a boolean-returning function that determines which partition an element belongs to. The function should return true for elements that belong to the first partition, and false for elements that belong to the second partition.

In the example above, the array is partitioned into two partitions: one with even numbers, and one with odd numbers. The resulting partitions are destructured into even and odd variables using array destructuring. The types of the partitions are inferred from the input array because they have the same type.

Using type annotations, you can specify the types of the input array and the partitioned arrays as follows:

index.ts
import { partition } from 'underscore';

const arr: number[] = [1, 2, 3, 4, 5];
const [even, odd]: [number[], number[]] = partition(arr, (num: number) => num % 2 === 0);

console.log(even); // [2, 4]
console.log(odd); // [1, 3, 5]
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In the example above, we have specified that even and odd are arrays of numbers using type annotations. The types of the input and output arrays are checked at compile time, which can help catch errors early in development.