數組的幾種常用方法
// //unshift()添加,將要給定的數值添加到數組的開頭
// var arr1=["王白菜","牛春","野老多"];
// console.log(arr1.unshift("大臉","老安"));//5
// console.log(arr1);
// // ["大臉", "老安", "王白菜", "牛春", "野老多"]
// var arr = [1, 2];
//// arr.unshift(0);
//// arr.unshift(-2, -1); //-2, -1, 0, 1, 2
// arr.unshift([-3]);
// console.log(arr);
//shift() 方法從數組中刪除第一個元素，並返回該元素的值。此方法更改數組的長度。
//從數組中刪除的元素; 如果數組為空則返回undefined 。
// let a = [1, 2, 3];
// let b = a.shift();
// console.log(a);
// // [2, 3]
// console.log(b);
// // 1
// //push()添加,將要給定的數值添加到數組的后頭
// var arr2=["王白菜","牛春","野老多"];
// console.log(arr2.push("大臉","老安"));//5
// console.log(arr2);//"王白菜", "牛春", "野老多", "大臉", "老安"
//pop()方法從數組中刪除最后一個元素，並返回該元素的值。此方法更改數組的長度。
//let a = [1, 2, 3];
//a.length; // 3
//a.pop(); // 3
//console.log(a); // [1, 2]
//a.length; // 2
// splice(起點[從1開始],(長度[不刪除就為0,刪除幾個就是幾個],元素A,元素B)
var arr=["王白菜","牛春","野老多"];
// arr.splice(1, 0, '老安');
// console.log(arr);//"王白菜", "老安", "牛春", "野老多"
//想從哪一個后面開始添加就寫幾
//例如從第一位后開始添加"老安","平板"，
// arr.splice(1, 0, "老安","平板");
// console.log(arr);//"王白菜", "老安", "平板", "牛春", "野老多"
// 從第一位后刪除牛春，添加"老安","平板"，
// arr.splice(1, 1, "老安","平板");
// console.log(arr);//"王白菜", "老安", "平板", "野老多
// arr.splice(1, 0);
// console.log(arr); //"王白菜","牛春","野老多"
//concat()合並，將兩個數組合並
var arr1 = ['a', 'b', 'c'];
var arr2 = ['d', 'e', 'f'];
//=======合並=====
// console.log(arr1.concat(arr2));//["a", "b", "c", "d", "e", "f"]
//========方法一========
// console.log(arr1.concat("j",arr2));//["a", "b", "c", "j", "d", "e", "f"]
// console.log(arr1.concat("j"+arr2));// ["a", "b", "c", "jd,e,f"]
// ===========方法2===========
// console.log(arr1+arr2.concat("j"));//拼接在一起a,b,cd,e,f,j
// //join()將數組（或一個類數組對象）的所有元素變成字符串
// var arr2=["王白菜","牛春","野老多"];
// console.log(arr2.join());//王白菜,牛春,野老多
// console.log(arr2.join(''));//王白菜牛春野老多
// console.log(arr2.join('-'));//王白菜-牛春-野老多
// //reverse()方法是將數組順序顛倒
// var arr = ['one', 'two', 'three'];
// var reversed = arr.reverse();
// console.log(arr);//["three", "two", "one"]
//// console.log(reversed);
// //sort()排序
// var arr = [1, 30, 22, 49, 31, 21];
//// arr.sort();
//// console.log(arr);//[1, 21, 22, 30, 31, 49]
// arr.sort(function(a, b) {
//// return a - b;//升序[1, 21, 22, 30, 31, 49]
// return b - a;//降序[49, 31, 30, 22, 21, 1]
// });
// console.log(arr);
// filter()數組的過濾
// 例子:過濾出數組中單詞長度大於6的單詞
// let words = ['spr', 'limit', 'like', 'destruction', 'present'];
// let result = words.filter(word => word.length > 6);
// console.log(result)