数组的用法(大部分ES6)

1:map

返回每一项的映射，生成一个新的数组;

2:isArray

Array.isArray(arr);
返回 boolean值;

find,findIndex,

返回数组中满足条件的第一个元素的值，否则undefined;

keys()

类似Obeject.keys();

entries

 let  arr = [ 1,2,3,10,20,30]
 let iterator = arr.entries()
 console.log(iterator.next())
 console.log(iterator.next())
 console.log(iterator.next());
 返回可迭代对象，使用next()方法即可使用;

includes

let  arr = [ 1,2,3,10,20,30]
      let iterator = arr.includes(30)
      console.log(iterator)；//true

reduce

    let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice'];

    let nameNum = names.reduce((pre, cur) => {

      console.log('当前的值',cur)
      if (cur in pre) {
        pre[cur]++
      } else {
        pre[cur] = 1
      }
      return pre
    }, {});
    // initiVal:作为第一次调用callback函数时第一个参数的值;
    console.log(nameNum); //{Alice: 2, Bob: 1, Tiff: 1, Bruce: 1}