Sometimes, we may want to get the closest number to a given number out of a JavaScript array.
In this article, we’ll look at how to get the closest number to a number out of a JavaScript array.
Using the Array.prototype.reduce Method
One way to get the closest number to a number out of a JavaScript array is to use the JavaScript array’s reduce method.
To use it, we write:
const arr = [2, 42, 82, 122, 162, 202, 242, 282, 322, 362]
const goal = 100
const closest = arr.reduce((prev, curr) => {
return (Math.abs(curr - goal) < Math.abs(prev - goal) ? curr : prev);
});
console.log(closest)
We have the arr array that has a bunch of numbers.
goal is the number that we want to find the closest number in arr from.
We then pass in the callback into the reduce method that compares the absolute value of the difference between curr — goal and prev-goal .
prev is the previously closest number to goal .
And curr is the current number that’s being iterated through.
If curr is closer to goal that prev in absolute value, then we return curr .
Otherwise, we return goal .
Therefore, closest is 82.
Use the Array.prototype.map Method
Another way to find the closest number to a given number is to map all the array entries to the absolute difference between the number in the array and the goal number.
Then we can use Math.min to find the minimum difference between the numbers.
For instance, we can write:
const arr = [2, 42, 82, 122, 162, 202, 242, 282, 322, 362]
const goal = 100
const indexArr = arr.map((num) => {
return Math.abs(num - goal)
})
const min = Math.min(...indexArr)
const closest = arr[indexArr.indexOf(min)]
console.log(closest)
We call map with a callback that returns the absolute difference between num and goal .
Then we find the minimum of the differences with Math.min .
And then we get the index of the number with the lowest absolute difference with indexOf and pass that into arr to get the number that’s closest to goal .
So we get the same result as the previous example.
Conclusion
We can use JavaScript array and math methods to get the number that’s closest to the given number in an array with JavaScript.
