5个数组Array方法: indexOf、filter、forEach、map、reduce使用实例

在ES5中，一共有9个Array方法 :

Array.prototype.indexOf
Array.prototype.lastIndexOf
Array.prototype.every
Array.prototype.some
Array.prototype.forEach
Array.prototype.map
Array.prototype.filter
Array.prototype.reduce
Array.prototype.reduceRight

1. indexOf

var arr = ['apple','orange','pear'];

console.log("found:", arr.indexOf("orange") );

found: 1

2. filter

var arr = [
{"name":"apple", "count": 2},
{"name":"orange", "count": 5},
{"name":"pear", "count": 3},
{"name":"orange", "count": 16},
];

var newArr = arr.filter(function(item){
return item.name=='orange';
})

console.log("Filter results:",newArr.toString());

Filter results: [{"name":"orange","count":5},{"name":"orange","count":16}]

3. forEach

var arr = [1,2,3,4,5,6,7,8];

arr.forEach(function(item,index){
console.log("item:"+item+",index:"+index);
});

item:1,index:0
item:2,index:1
item:3,index:2
item:4,index:3
item:5,index:4
item:6,index:5
item:7,index:6
item:8,index:7

4. map()

var oldArr =
[{first_name:"Colin",last_name:"Toh"},
{first_name:"Addy",last_name:"Osmani"},
{first_name:"Yehuda",last_name:"Katz"}];

function getNewArr(){
return oldArr.map(function(item,index){
item.full_name = [item.first_name,item.last_name].join(" ");
return item;
});
}
console.log(getNewArr());

[{"first_name":"Colin","last_name":"Toh","full_name":"Colin Toh"},{"first_name":"Addy","last_name":"Osmani","full_name":"Addy Osmani"},{"first_name":"Yehuda","last_name":"Katz","full_name":"Yehuda Katz"}]

5. reduce()

var arr = ["apple","orange","apple","orange","pear","orange"];

function getWordCnt(){
return arr.reduce(function(prev,next){
console.log("prev:"+JSON.stringify(prev)+",next:"+next)
prev[next] = (prev[next] + 1) || 1;
return prev;
},{});
}

console.log(JSON.stringify(getWordCnt()));

prev:{},next:apple
prev:{"apple":1},next:orange
prev:{"apple":1,"orange":1},next:apple
prev:{"apple":2,"orange":1},next:orange
prev:{"apple":2,"orange":2},next:pear
prev:{"apple":2,"orange":2,"pear":1},next:orange
VM401:11 {"apple":2,"orange":3,"pear":1}