Get host machine endianness using JavaScript Typed Arrays (polyfill for `os.endianness()` in node.js)

endianness.js

function endianness () {
  var b = new ArrayBuffer(4);
  var a = new Uint32Array(b);
  var c = new Uint8Array(b);
  a[0] = 0xdeadbeef;
  if (c[0] == 0xef) return 'LE';
  if (c[0] == 0xde) return 'BE';
  throw new Error('unknown endianness');
}

endianness();
// "LE"


// A shorter version
var a = new Uint32Array([0x12345678]);
var b = new Uint8Array(a.buffer, a.byteOffset, a.byteLength);
var BigEndian = (b[0] == 0x12);