Find the number in an array that is closest to a given number

Question

I have an Array of integers in javascript, [5,10,15,20,25,30,35] when given a number x, how can I find the element in the array that is closest to that number?

Answer 1

Since Array.reduce is a reality for so long (even IE9 supports it), the problem is easily solvable with it. This way, no need to sort the array first (no array mutation at all):

var numbers = [20, 25, 30, 35, 5, 10, 15], x = 7;

var output = numbers.reduce(function (prev, curr) {
  return Math.abs(curr - x) < Math.abs(prev - x) ? curr : prev
});

console.log(output);

You can go further and solve it with only one line of ES6 (ECMAScript 2015) syntax, by using an arrow function (but with no IE support in this case):

const numbers = [20, 25, 30, 35, 5, 10, 15], x = 7;

const output = numbers.reduce((prev, curr) => Math.abs(curr - x) < Math.abs(prev - x) ? curr : prev);

console.log(output);

Of course, for flexibility and reusability, it's easy to make it as a function:

const closest = (array, goal) => array.reduce((prev, curr) => Math.abs(curr - goal) < Math.abs(prev - goal) ? curr : prev);

console.log(closest([20, 25, 30, 35, 5, 10, 15], 7));
console.log(closest([20, 25, 30, 35, 5, 10, 15], 8));
console.log(closest([1, 5, 7], -5));
console.log(closest([1, 5, 7], 4));
console.log(closest([1, 5, 7], 20));