Interpolation_Search.js

// Function for Interpolation search
function Interpolation_Search(array, search_item)
{
    var low = 0;
    var high = array.length - 1;
    var pos;

    while (low <= high && search_item >= array[low] && search_item <= array[high])
    {
        var rise = high - low;
        var run = array[high] - array[low];
        var x = search_item - array[low];

        pos = low + Math.floor(rise / run) * x;

        if (array[pos] === search_item)
            return pos;

        else if (search_item < array[pos])
            high = pos - 1;

        else if (search_item > array[pos])
            low = pos + 1;
    }

    return -1;
}

var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];


var search_item = 5;

var index = Interpolation_Search(array, search_item);

if (index !== -1)
    console.log("found at position " + (index + 1));
else
    console.log("Not found");



/* Output

Found at position 5

*/