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

The foldl function in the Underscore library can be used in TypeScript as follows:

index.ts
import * as _ from 'underscore';

const arr: number[] = [1, 2, 3, 4, 5];

const sum: number = _.foldl(arr, (memo: number, num: number) => {
  return memo + num;
}, 0);

console.log(sum); // Output: 15
201 chars
10 lines

Explanation:

1. Import the underscore library using import * as _ from 'underscore';
2. Declare an array arr containing some numbers
3. Call the foldl function on the array arr passing three parameters:
   • The input array arr
   • A function that takes two parameters:
     • memo: This parameter represents the accumulated result from previous iterations.
     • num: This parameter represents the current element of the array being processed.
     • The function returns the updated memo value after processing the current element.
   • An initial value to begin the accumulation. In this case, we start the accumulation with 0.
4. The foldl function iterates over the array arr and applies the function provided in step 3 to each element, accumulating the result as it goes.
5. Finally, the accumulated result is stored in the sum variable.
6. We log the value of sum to the console, which will output 15, as expected.

Note: Underscore is a third-party library and needs to be installed through NPM or added as a script tag in your HTML file. Additionally, as foldl is a part of the functional programming paradigm, this can be used in any language which supports high-order functions including JavaScript and TypeScript.