Array数组对象中的forEach、map、filter及reduce详析

var map = new Map();
map.set('item1', 'value1')
map.set('item2', 'value2')
map.forEach(function(value, key, map) {
 console.log("Key: %s, Value: %s", key, value);
});

var new_arr = arr.filter(callback(element, index, array){

}, this)

//如果返回值是true的话，就是符合条件。
//filter 不会改变原数组，它返回过滤后的新数组。
//这个里返回数组里面的偶数
[10,11,12,13].filter((v)=>v % 2 == 0)
//只要审核通过的。当然正常情况下，对象比这个复杂一些。
[{state:1},{state:0},{state:0},{state:0}].filter((v)=>v.state == 1)
//只要成年人，记录是有效的
[{age:18,state:1},{age:16,state:0},{age:21,state:0}].filter((v)=>v.state == 1 && v.age > 17)

arr.forEach(callback(element, index, array){

}, this)

//遍历数组。打印到控制台
[10,11,12,13].forEach((v)=>{
 console.log(v)
})
// 成功的收集到success里面,错误的收集到error里面。
var success = [],error = [];
[{state:1},{state:0},{state:0},{state:0}].forEach((v)=>{
 if(v.state == 1){
  success.push(v)
 }else{
  error.push(v)
 }
})
// 给20岁的小姐姐打招呼
[{state:1,age: 1},{state:0,age: 20},{state:0,age: 19},{state:0,age: 31}].forEach((v)=>{
 if(v.age == 20){
  console.log('你好啊，我今年正好80')
 }
})

arr.map(callback(element, index, array){

}, this)

//把数值格式化，保留两位小数
[10.055,11.054,12.056,13.789].map((v)=>+v.toFixed(2))

arr.reduce(callback(accumulator, element, index, array){

}, initialValue)

//累加
[10,11,12,13].reduce((s,v)=>s+v,0)

[{name: 'l1', phone: '1507539'},{name: 'l2', phone: '1507540'},{name: 'l3', phone: '1507541'},{name: 'l4', phone: '1507538'}]
 .sort((n,m)=>n.phone<m.phone)
 .map(m=>m.name)
 .join(',')

 [].slice.call(document.querySelectorAll('div'))
 .forEach(v=>v.addEventListener('click',e=>console.log(e.target.className)))

[].slice.call(document.querySelectorAll('*'))
 .map(v=>v.className)
 .filter(v=>v)