freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/es6/write-higher-order-arrow-functions.english.md

id	title	challengeType
587d7b88367417b2b2512b45	Write Higher Order Arrow Functions	1

Description

It's time we see how powerful arrow functions are when processing data. Arrow functions work really well with higher order functions, such as map(), filter(), and reduce(), that take other functions as arguments for processing collections of data. Read the following code:

FBPosts.filter(function(post) {
  return post.thumbnail !== null && post.shares > 100 && post.likes > 500;
})

We have written this with filter() to at least make it somewhat readable. Now compare it to the following code which uses arrow function syntax instead:

FBPosts.filter((post) => post.thumbnail !== null && post.shares > 100 && post.likes > 500)

This code is more succinct and accomplishes the same task with fewer lines of code.

Instructions

Use arrow function syntax to compute the square of only the positive integers (decimal numbers are not integers) in the array realNumberArray and store the new array in the variable squaredIntegers.

Tests

tests:
  - text: <code>squaredIntegers</code> should be a constant variable (by using <code>const</code>).
    testString: getUserInput => assert(getUserInput('index').match(/const\s+squaredIntegers/g), '<code>squaredIntegers</code> should be a constant variable (by using <code>const</code>).');
  - text: <code>squaredIntegers</code> should be an <code>array</code>
    testString: assert(Array.isArray(squaredIntegers), '<code>squaredIntegers</code> should be an <code>array</code>');
  - text: <code>squaredIntegers</code> should be <code>[16, 1764, 36]</code>
    testString: assert.deepStrictEqual(squaredIntegers, [16, 1764, 36], '<code>squaredIntegers</code> should be <code>[16, 1764, 36]</code>');
  - text: <code>function</code> keyword was not used.
    testString: getUserInput => assert(!getUserInput('index').match(/function/g), '<code>function</code> keyword was not used.');
  - text: loop should not be used
    testString: getUserInput => assert(!getUserInput('index').match(/(for)|(while)/g), 'loop should not be used');
  - text: <code>map</code>, <code>filter</code>, or <code>reduce</code> should be used
    testString: getUserInput => assert(getUserInput('index').match(/map|filter|reduce/g), '<code>map</code>, <code>filter</code>, or <code>reduce</code> should be used');

Challenge Seed

const realNumberArray = [4, 5.6, -9.8, 3.14, 42, 6, 8.34, -2];
const squareList = (arr) => {
  "use strict";
  // change code below this line
  const squaredIntegers = arr;
  // change code above this line
  return squaredIntegers;
};
// test your code
const squaredIntegers = squareList(realNumberArray);
console.log(squaredIntegers);

Solution

const realNumberArray = [4, 5.6, -9.8, 3.14, 42, 6, 8.34, -2];
const squareList = (arr) => {
  "use strict";
  // change code below this line
  const squaredIntegers = arr.filter(num => Number.isInteger(num) && num > 0).map((x) => x * x);
  // change code above this line
  return squaredIntegers;
};
// test your code
const squaredIntegers = squareList(realNumberArray);
console.log(squaredIntegers);