function openArray(array) {
    array.reduce(function(result, current) {
        if(Array.isArray(current)) {
            result.concat(openArray(current));
        } else {
            result.concat(current);
        }
    });
}

function openArray(array) {
    let newArray = [];
    return array.reduce(function(result, current) {
        console.log(result)
        console.log(current)
        if(Array.isArray(current)) {
            newArray = result.concat(openArray(current));
        } else {
            newArray = result.concat(current);
        }
    });
}

const openArray = array => array.reduce((result, current) => Array.isArray(current) ? result.concat(expand(current)) : result.concat(current), []);