Flat the nested array

array_flatter.js

function flatter(data) {
    var result = [];
    for (var i = 0; i < data.length; i++) {
        if(Array.isArray(data[i])) {
            result = result.concat(flatten(data[i]));
        } else {
            result.push(data[i]);
        }
    }
    return result;
}

console.log(flatter([[1,2,[1,2,3]],4]));