列表的基础实现

构建通用方法去实现增删改查以及遍历。这是一个思想，可以借鉴一下。

function List() {
  this.listSize = 0// 列表元素个数
  this.pos = 0
  this.dataSource = []
  this.append = append
  this.remove = remove
  this.find = find
  this.toString = toString
  this.clear = clear
  this.insert = insert
  this.front = front
  this.end = end
  this.prev = prev
  this.next = next
  this.length = length
  this.currPos = currPos
  this.moveTo = moveTo
  this.getElement = getElement
  this.length = length
  this.contains = contains
}
function append(element) {
  this.dataSource[this.listSize] = element
  this.listSize += 1
}
function find(element) {
  for (let i = 0; i < this.dataSource.length; ++i) {
    if (this.dataSource[i] === element) {
      return i
    }
    return -1
  }
}
function remove(element) {
  console.log(this)
  var foundAt = this.find(element)
  //  先找到对应的位置，然后用splice删除，同时将长度-1
  if (foundAt > -1) {
    this.dataSource.splice(foundAt, 1)
    this.listSize -= 1
    return true
  }
  return false
}
function length() {
  return this.listSize
}
function toString() {
  return this.dataSource
}
function insert(element, after) {
  var insertPos = this.find(after)
  if (insertPos > -1) {
    this.dataSource.splice(insertPos + 1, 0, element)
    ++this.listSize
    return true
  }
  return false
}
function clear() {
  delete this.dataSource
  this.dataSource = []
  this.listSize = 0
  this.pos = 0
}
function contains(element) {
  for (let i = 0; i < this.dataSource.length; ++i) {
    if (this.dataSource[i] === element) {
      return true
    }
    return false
  }
}
function front() {
  this.pos = 0
}
function end() {
  this.pos = this.listSize - 1
}
function prev() {
  if (this.pos > 0) {
    --this.pos
  }
}
function next() {
  if (this.pos < this.listSize - 1) {
    ++this.pos
  }
}
function currPos() {
  return this.pos
}
function moveTo(position) {
  this.pos = position
}
function getElement() {
  return this.dataSource[this.pos]
}
var listFun = new List()
listFun.append('&&')
console.log(listFun.toString)
listFun.remove('&&')
listFun.append('&2&')
listFun.append('2&2&')
listFun.append('22')
listFun.front()
console.log(listFun.getElement())
listFun.next()
console.log(listFun.getElement())
listFun.next()
listFun.next()
listFun.prev()
console.log(listFun.getElement())

// 你看用自己写的方法，完成遍历
for (listFun.front(); listFun.currPos() < listFun.length(); listFun.next()) {
  console.log(listFun.getElement())
}
// 倒序的遍历
for (listFun.end(); listFun.currPos() >= 0; listFun.prev()) {
  console.log(listFun.getElement())
}