<p>each1</p>
<p>each2</p>
<p>each3</p>
...
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
<script>
var arr = [1,2,3]
var nodeList = document.getElementsByTagName('p')
var $p = $('p')
// 如果要對這三個變量進行遍歷，需要寫三個遍歷方法
// 1
arr.forEach(function(item){
	console.log(item)
})
// 2
var i;length = nodeList.length
for(i = 0;i < length;i ++) {
	console.log(nodeList(i))
}
// 3
$p.each(function(key, p){
	console.log(key,p)
})
</script>

// 如果寫成一個遍歷方法，拿jquery的$.each舉例，則這種方法稱為迭代器模式
var arr = [1,2,3]
var nodeList = document.getElementsByTagName('p')
var $p = $('p')
function each(data){
	var $data = data
	$data.each(function(key, val){
		console.log(key, val)
	})
}
each(arr)
each(nodeList)
each($p)

class Iterator {
    constructor(conatiner) {
        this.list = conatiner.list
        this.index = 0
    }
    next() {
        if (this.hasNext()) {
            return this.list[this.index++]
        }
        return null
    }
    hasNext() {
        if (this.index >= this.list.length) {
            return false
        }
        return true
    }
}
class Container {
    constructor(list) {
        this.list = list
    }
    getIterator() {
        return new Iterator(this)
    }
}
// 測試代碼
let container = new Container([1, 2, 3, 4, 5])
let iterator = container.getIterator()
while(iterator.hasNext()) {
    console.log(iterator.next())
}

let arr = [1, 2, 3, 4]
let nodeList = document.getElementsByTagName('p')
let m = new Map()
m.set('a', 100)
m.set('b', 200)
function each(data) {
    // 生成遍歷器
    let iterator = data[Symbol.iterator]()
    let item = {done: false}
    while (!item.done) {
        item = iterator.next()
        if (!item.done) {
            console.log(item.value)
        }
    }
}
each(arr)
each(nodeList)
each(m)

function each(data) {
    for (let item of data) {
        console.log(item)
    }
}
each(arr)
each(nodeList)
each(m)