docs(arraybuffer): edit arraybuffer

docs/arraybuffer.md

@@ -454,7 +454,17 @@ Float64Array.BYTES_PER_ELEMENT // 8
 function ab2str(buf) {
   // 注意，如果是大型二进制数组，为了避免溢出，
   // 必须一个一个字符地转
-  return String.fromCharCode.apply(null, new Uint16Array(buf));
+  if (buf && buf.byteLength < 1024) {
+    return String.fromCharCode.apply(null, new Uint16Array(buf));
+  }
+
+  const bufView = new Uint16Array(buf);
+  const len =  bufView.length;
+  const bstr = new Array(len);
+  for (let i = 0; i < len; i++) {
+    bstr[i] = String.fromCharCode.call(null, bufView[i]);
+  }
+  return bstr.join('');
 }
 
 // 字符串转为 ArrayBuffer 对象，参数为字符串