buckets.js

// you can use console.log for debugging purposes, i.e.
// console.log('this is a debug message');

function solution(X, A) {
    // write your code in JavaScript (ECMA-262, 5th edition)
    var isNotEqual = 0;
    A.forEach(function(item) {
        if (item !== X) {
            isNotEqual++;
        }
    });
    // to understand the problem a little better 
    var bucket1 = isNotEqual;
    var bucket2 = 0; 
    var returnValue = -1;
    // make equal buckets
    A.some(function(item, index) {
        if (item === X) {
            bucket2++
        } else {
            bucket1--;
        }
        
        if (bucket1 === bucket2 && (bucket1 !== 0 && bucket2 !== 0)) {
            returnValue = index + 1;
            return true;
        } 
    });
    
    return returnValue;

}