JavaScript数组操作总结

const arr = [0,'1',{},function(){}];
//二维数组
const arr1 = [1,2,[3,4,5],6];

const arr = [];
arr['1'] = 1;
//1被自动转换成'1'
console.log(arr[1],arr['1']); //1
typeof arr; //obejct

const arr = [];
arr[2.1] = 2.1;
arr['a'] = 'a';
console.log(arr); //[2.1: 2.1, a: 'a']
console.log(arr.length); //0

const arr = [1,2,3,4,5];
arr.length = 2;
console.log(arr); //[1,2]

const arr = ['a','b'];
1 in arr; // true
2 in arr; //fasle

const arr = [1,2];
arr['a'] = 3;
arr[4.5] = 4;
for(key in arr){
 console.log(key);
};
// 0
// 1
// a
/  4.5
Object.keys(arr); // ['0', '1', 'a', '4.5']

var arr = [1,5,,8];
console.log(arr); //[1, 5, empty, 8]
//使用delete也会产生空值
delete arr [0];
console.log(arr); //[empty, 5, empty, 8]
console.log(arr.length); //4

    const arr1 = new Array(10); //[empty × 10]
    for (key in arr1) {
      console.log(arr1);
    }; //无输出,没有进行遍历
    arr1.forEach((v) => {
      console.log(v)
    }); //无输出,没有进行遍历
    console.log(Object.keys(arr1)); //[]
    const arr2 = [undefined, undefined, undefined]; //[empty × 10]
    for (key in arr2) {
      console.log(key);
    };
    //0
    //1
    //2
    arr2.forEach((value, index) => {
      console.log(value, index)
    });
    // undefined,0
    // undefined,1
    // undefinef,2
    console.log(Object.keys(arr2)); //[3]
    // 使用for循环遍历empty
    for(let i = 0;i<arr1.length;i++){
       console.log(arr1[1])
    };
    //undefined × 10

const arrayLike = { 
  0:'a', 
  1:'b', 
  2:'c', 
  length:3 
  };
arrayLike[3] = 'd';
console.log(arrayLike[0]); //a
console.log(arrayLike.length); //3

function foo(){
  console.log(arguments);
};
foo('tom','jack');
// {0:'tom', 1:'jack', length:2, callee:...}
console.log(document.getElementsByClassName('a'));
//{"0": ...,"1": ...,"2":..., "length":3}
const str = 'apple';
console.log(str.length); //5
consoel.log(str[2]); //p

function foo(){
  const arr = Array.prototype.slice.call(arguments);
}
function foo(){
  const arr = [...arguments]
}
function foo(...args){
}