var arr = [
  ['h', 'e', 'l', 'l', 'o'],
  ['m', 'y'],
  ['w', 'o', 'r', 'l', 'd'],
  ['!']
];
var result = [];
for (var r = 0; r < arr.length; r++) {
  for (var c = 0; c < arr[r].length; c++) {
    result.push(arr[r][c]);
  }
}
console.log(result); //=>[ 'h', 'e', 'l', 'l', 'o', 'm', 'y', 'w', 'o', 'r', 'l', 'd', '!' ]

var arr = [
  ['h', 'e', 'l', 'l', 'o'],
  ['m', 'y'],
  ['w', 'o', 'r', 'l', 'd'],
  ['!']
];
var result = [];
for (var r = 0, result = []; r < arr.length; r++) {
  result = result.concat(arr[r]);
}
console.log(result); //=>[ 'h', 'e', 'l', 'l', 'o', 'm', 'y', 'w', 'o', 'r', 'l', 'd', '!' ]

var arr = [
  ['h', 'e', 'l', 'l', 'o'],
  ['m', 'y'],
  ['w', 'o', 'r', 'l', 'd'],
  ['!']
];
var result = Array.prototype.concat.apply([], arr);
console.log(result); //=>[ 'h', 'e', 'l', 'l', 'o', 'm', 'y', 'w', 'o', 'r', 'l', 'd', '!' ]

Array.prototype.deepFlatten = function() {
  var result = []; //定义保存结果的数组
  this.forEach(function(val, idx) { //遍历数组
    if (Array.isArray(val)) { //判断是否为子数组
      val.forEach(arguments.callee); //为子数组则递归执行
    } else {
      result.push(val); //不为子数组则将值存入结果数组中
    }
  });
  return result; //返回result数组
}
var arr = [2, 3, [2, 2],
  [3, 'f', ['w', 3]], { "name": 'Tom' }
];
console.log(arr.deepFlatten()); //=>[ 2, 3, 2, 2, 3, 'f', 'w', 3, { name: 'Tom' } ]

Array.prototype.deepFlatten = function() {
  var result = []; //定义保存结果的数组
  var stack = this; //将数组放入栈中
  while (stack.length !== 0) { //如果栈不为空，则循环遍历
    var val = stack.pop(); //取出最后一个值
    if (Array.isArray(val)) { //判断是不是数组
      stack = stack.concat(val); //如果是数组就将拼接入栈中
    } else {
      result.unshift(val); //如果不是数组就将其取出来放入结果数组中
    }
  }
  return result;
}
var arr = [2, 3, [2, 2],
  [3, 'f', ['w', 3]], { "name": 'Tom' }
];
console.log(arr.deepFlatten()); //=>[ 2, 3, 2, 2, 3, 'f', 'w', 3, { name: 'Tom' } ]