JavaScript基础之Array?forEach使用示例

var list = ["云层上的光", "初心", "栾树"];
list.forEach(function(item, index, array){
    console.log(item,index,array)
});

var list = ["云层上的光", "初心", "栾树"];
var value = list.forEach(function(item, index, array){
    console.log(this);
});
console.log(value);

Array.prototype.myForEach = function (callback) {
  var _arr    = this,// 调用时谁 this就是谁
      _len    = _arr.length,
      thisArg = arguments[1] || window;
  // 校验callback之能是 function时才往下执行
  if (typeof callback !== 'function') {
    throw new Error(`${callback} is not a function`);
  }
  // for循环
  for (var i = 0; i < _len; i++) {
    callback.apply(thisArg, [_arr[i], i, _arr]);
  }
  // 注意 forEach 没有返回值
}

const arrayLike = {
  length: 3,
  0: 2,
  1: 3,
  2: 4,
};
Array.prototype.forEach.call(arrayLike, (x) => console.log(x));

var list = ["云层上的光", "初心", "栾树"];
try{
    list.forEach(item=>{
        if(item === "初心") throw new Error("初心");
    })
}catch(err){
    if(err.message === "初心")	
        console.log("在执行到初心时跳出循环体了")
    else 
        console.error(err)
}