2724-SortBy.js

// 2724. Sort By
// Given an array arr and a function fn, return a sorted array sortedArr. 
// You can assume fn only returns numbers and those numbers determine the sort order of sortedArr. 
// sortedArray must be sorted in ascending order by fn output.
// You may assume that fn will never duplicate numbers for a given array.

// Example 1:
// Input: arr = [5, 4, 1, 2, 3], fn = (x) => x
// Output: [1, 2, 3, 4, 5]
// Explanation: fn simply returns the number passed to it so the array is sorted in ascending order.

// Example 2:
// Input: arr = [{"x": 1}, {"x": 0}, {"x": -1}], fn = (d) => d.x
// Output: [{"x": -1}, {"x": 0}, {"x": 1}]
// Explanation: fn returns the value for the "x" key. So the array is sorted based on that value.

// Example 3:
// Input: arr = [[3, 4], [5, 2], [10, 1]], fn = (x) => x[1]
// Output: [[10, 1], [5, 2], [3, 4]]
// Explanation: arr is sorted in ascending order by number at index=1. 

// Constraints:
//         arr is a valid JSON array
//         fn is a function that returns a number
//         1 <= arr.length <= 5 * 10^5

/**
 * @param {Array} arr
 * @param {Function} fn
 * @return {Array}
 */
var sortBy = function(arr, fn) {
    return arr.sort((a,b) => fn(a) - fn(b));
};

console.log(sortBy([5, 4, 1, 2, 3],(x) => x)) // [1, 2, 3, 4, 5]
console.log(sortBy([{"x": 1}, {"x": 0}, {"x": -1}],(d) => d.x)) // [{"x": -1}, {"x": 0}, {"x": 1}]
console.log(sortBy([[3, 4], [5, 2], [10, 1]],(x) => x[1])) // [[10, 1], [5, 2], [3, 4]]