Array數組對象中的forEach、map、filter及reduce詳析

//如果返回值是true的話，就是符合條件。
//filter 不會改變原數組，它返回過濾后的新數組。
//這個里返回數組里面的偶數
[10,11,12,13].filter((v)=>v % 2 == 0)
//只要審核通過的。當然正常情況下，對象比這個復雜一些。
[{state:1},{state:0},{state:0},{state:0}].filter((v)=>v.state == 1)
//只要成年人，記錄是有效的
[{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)

//遍歷數組。打印到控制臺
[10,11,12,13].forEach((v)=>{
 console.log(v)
})
// 成功的收集到success里面,錯誤的收集到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)
 }
})
// 給20歲的小姐姐打招呼
[{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)

//把數值格式化，保留兩位小數
[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)