Flat array, one-dimensional array variable multidimensional array

    // multidimensional array into a one-dimensional array 
    var MyArray1 = [[l, 2,3], [4,5,6]] 
    function Flatten (ARR) { 
        return arr.join ( ','). Split ( ', ') .map (function (Item) { 
            return the parseInt (Item); 
        }) 
    } 
    var B = Flatten (MyArray1); 
    the console.log (B);

 arr.join ( ',') 123456 array into a string

arr.join ( ','). split ( ',') split () method for dividing a character string into a string array. [ "1", "2", "3", "4", "5", "6"]

arr.join(',').split(',').map(function (item) {

　　　　return parseInt(item);　　　　　　[1,2,3,4,5,6]

})