不固定个数组，进行一一对应的组合,js将多个数组实现排列组合

var arr = [
            ["a", "b"],
            ["1", "2"],
            ["d"]
        ];
        var sarr = [
            []
        ];
        for (var i = 0; i < arr.length; i++) {
            var tarr = [];
            for (var j = 0; j < sarr.length; j++)
                for (var k = 0; k < arr[i].length; k++)
                    tarr.push(sarr[j].concat(arr[i][k]));
            sarr = tarr;
        }
        alert(sarr.join("\n"));