Find the closest smaller value of an array

Question

I think what I want is pretty simple but I can't really find the correct solution.

I have this kind of array in Javascript :

[0, 38, 136, 202, 261, 399]

And I get a generated value from 0 to 600 on a button click. What I need is to find the nearest lower value in this array.

For example, if the generated value is 198, I want to get 136 as the result. If the generated value is 300, I want 261... If it's 589, I want 399 etc etc.

Until now, I have tried with this code :

var theArray = [ 1, 3, 8, 10, 13 ];
var goal = 7;
var closest = null;

$.each(theArray, function(){
    if (closest == null || Math.abs(this - goal) < Math.abs(closest - goal)) {
        closest = this;
    }
});

alert(closest);

But it only returns the closest value... Now I need the to get only the closest smaller value for the given number... How can I improve my algorithm to fit my needs?

Thanks!

Answer 1

Reverse the array and use find

let arr = [0, 38, 136, 202, 261, 399];
let val = 300;
let number = arr.reverse().find(e => e <= val);
console.log(number);

Answer 2

If you array is sorted, and small enough, a really simple mode to do what you want it's simplly iterate over the array until number > number-in-array then return the number on the previous position.

function getClosestValue(myArray, myValue){
    //optional
    var i = 0;

    while(myArray[++i] < myValue);

    return myArray[--i];
}

Regards.