数组的五中遍历方式（forEach，filter，map，some，every）

forEach 遍历所有的元素，没有返回值, return 不会终止循环，只会结束本次循环，进行下一轮。

let ary = [
  { name: ‘aa‘, age: 10 },
  { name: ‘bb‘, age: 11 },
  { name: ‘cc‘, age: 12 },
  { name: ‘dd‘, age: 13 },
  { name: ‘ee‘, age: 14 },
]

let ary1 = []
let re = ary.forEach((item, index, list) => {
  if (item.name === ‘aa‘) {
    return
  }
  ary1.push(item.name)
})
console.log(ary1)  // ["bb", "cc", "dd", "ee"]
console.log(re)  // undefined
console.log(ary) // (5)?[{…}, {…}, {…}, {…}, {…}]

let ary2 = ary.filter((item, index, list) => {
  return item.age > 12
})
console.log(ary2) // (2)?[{…}, {…}]
console.log(ary) // (5)?[{…}, {…}, {…}, {…}, {…}]

let isAge = ary.every((item, index, list) => {
  console.log(index)  // 0
  return item.age > 11
})
console.log(isAge)  // false

let existAge = ary.some((item, index, list) => {
  console.log(index) // 0 1 2
  return item.age > 11
})
console.log(existAge)  // true

let ary3 = ary.map((item, index, list) => {
  return item.age + 10
})
console.log(ary3) // [20, 21, 22, 23, 24]
console.log(ary)  // (5)?[{…}, {…}, {…}, {…}, {…}]