第6章 数组

  var arr=['a','b','c'];
  arr.forEach((val,index,array)=>{
    console.log(typeof index);//number
    console.log(val,index,array);
  })


  delete arr[1];
  console.log(arr)//['a',undefined,'c'];

  console.log(arr.constructor===Array);//true
  console.log(arr.__proto__===Array.prototype);//true;

  console.log(Object.prototype.toString.apply(arr)==='[object Array]');//true