how to use the flatten function from the lodash library in typescript

To use the flatten function from the Lodash library in TypeScript, first, you need to install the Lodash library in your project:

npm install lodash
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After installing the Lodash library, you need to import the flatten function from the library in your TypeScript code file:

index.ts
import { flatten } from 'lodash';
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The flatten function takes an array as input and returns a new array with all nested arrays flattened. Here's an example of how you can use the flatten function:

index.ts
const arr: (number | number[])[] = [1, [2, [3, [4]], 5]];

const flattenedArr: number[] = flatten(arr);

console.log(flattenedArr); // Output: [1, 2, 3, 4, 5]
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In the example above, we have an array arr with nested arrays. We pass this array to the flatten function, which returns a new array with all nested arrays flattened. We store this new flattened array in the flattenedArr variable and then log it to the console.

Note that because the flatten function can return an array with different types, we need to specify the type of the array as (number | number[])[] to account for both numbers and arrays of numbers. If you know that your array has a consistent type, you can use that instead.