function foo(bar) {
    if (bar > 1) {
       return [1,2,3];
    } else {
       return 1;
    }
}

function isArray(obj) {
  return Object.prototype.toString.call(obj) === '[object Array]';
}

if (my_value && typeof my_value === 'object' &&  typeof my_value.length === 'number' &&
!(my_value.propertyIsEnumerable('length')) { // my_value is truly an array! }

function isarray(my_value) {

    if (my_value && typeof my_value === 'object' &&  typeof my_value.length === 'number' &&
        !(my_value.propertyIsEnumerable('length'))
         { return true; }
    else { return false; }
}

if(foo(1) instanceof Array)
    // You have an Array
else
    // You don't

function is_array_compliant(obj){
    return obj && typeof obj.length != 'undefined';
}