JavaScript 数组方法filter与reduce

let arr1 = [1, 2, 3, 4, 5];
  let newArr1 = arr1.filter((item, index, thisArr) => {
    console.log(item);
    console.log(index);
    console.log(thisArr);
    return item > 2;
  })
  console.log(arr1);
  console.log(newArr1);`

// [1, 2, 3, 4, 5]  arr1
// [3, 4, 5]    newArr1

array.reduce(function(total,currentValue,currentIndex,thisArr){},initValue);
@function回调函数作为第一个参数，

// 数组求和
let arr1 = [1, 2, 3, 4, 5]
let totals = arr1.reduce(function (prev, next) {
    console.log(prev);
    console.log(next);
    return prev + next;
}, 0)
console.log(totals)

let arr = ['beep', 'boop', 'foo', 'bar'];
console.log(arr.reduce((acc, val) => (val[0] === 'b' && acc.push(val), acc), []));

// 进阶每个数是否含有'b'
arr.reduce((acc, val) =>
           (val.indexOf('b') >-1 && acc.push(val), acc),
           [])