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

To use the difference function from the lodash library in TypeScript, we first need to import it. Assuming we have installed the lodash library via npm, we can import it as follows:

index.ts
import * as _ from 'lodash';
29 chars
2 lines

With this import statement, we can now use the _.difference method to compare two arrays and return the elements that are only present in the first array. Here's how we can use the difference method in TypeScript:

index.ts
const array1 = [1, 2, 3, 4, 5];
const array2 = [3, 4, 5];

const diff = _.difference(array1, array2); // returns [1, 2]
120 chars
5 lines

Note that the _.difference method takes two arrays as arguments, and returns a new array containing the elements that are only present in the first array. Since TypeScript is a statically-typed language, it's a good practice to provide type declarations for the arrays that we are comparing. Here's an example:

index.ts
const array1: number[] = [1, 2, 3, 4, 5];
const array2: number[] = [3, 4, 5];

const diff: number[] = _.difference(array1, array2); // returns [1, 2]
150 chars
5 lines

With these type declarations, we can ensure that we are comparing arrays of numbers, and that the diff variable will also be an array of numbers.