# javascript - Fastest way to concatenate two JS uint8 arrays to a uint16 array?

I know this is fairly easy in other languages, but what is the best way to do this in JS if I have two arrays of 8-bit unsigned integers, and would like to concatenate them to one array of unsigned 16 bit integers?

Assuming both Arrays have the same length, use a `for` loop with the bitwise left shift operator `<<`;

``````var arr8A = [2, 3, 4], // example
arr8B = [5, 6, 7];
// code start
var arr16 = new Uint16Array(arr8A.length),
i;
for (i = 0; i < arr8A.length; ++i)
arr16[i] = (arr8A[i] << 8) + arr8B[i];
arr16;
``````

The reverse is similar but you use the bitwise zero-fill right shift operator `>>>` and the bitwise AND operator `&`;

``````// arr16 as above
var arr8A = new Uint8Array(arr16.length),
arr8B = new Uint8Array(arr16.length),
i;
for (i = 0; i < arr16.length; ++i) {
arr8A[i] = arr16[i] >>> 8;
arr8B[i] = arr16[i] & 255;
}
console.log(arr8A, arr8B);
``````

The maximum size numbers you can safely use these operators with are 32-bit integers.