var a = [1, 2, 2, 4, 1, 5, 5];
function answer (x) {
    var b = {};
    var i;
    for(i = 0; i < x.length; i++) {
        var c = x[i];
        if (c in b) {
            b[c] = b[c] + 1
        } else {
            b[c] = 1
        }
    }
    return b;
}

var d = answer(a);

console.log(d);