点击上方“逆锋起笔”,公众号回复 编程资源 领取大佬们推荐的学习资料
一、创建数组
var arr4 = []; //创建一个空数组
var arr5 = [20]; // 创建一个包含1项数据为20的数组
var arr6 = ["lily","lucy","Tom"]; // 创建一个包含3个字符串的数组
2、使用 Array 构造函数
无参构造
var arr1 = new Array(); //创建一个空数组
带参构造
var arr2 = new Array(20); // 创建一个包含20项的数组
var arr3 = new Array("lily","lucy","Tom"); // 创建一个包含3个字符串的数组
var array4 = new Array( 23 ); // ["23"]
3、Array.of 方法创建数组(es6 新增)
let arr = Array.of(1, 2);
console.log(arr.length);//2
let arr1 = Array.of(3);
console.log(arr1.length);//1
console.log(arr1[0]);//3
let arr2 = Array.of( 2 );
console.log(arr2.length);//1
console.log(arr2[0]);// 2
4、Array.from 方法创建数组(es6 新增)
function arga(...args) { //...args剩余参数数组,由传递给函数的实际参数提供
let arg = Array.from(args);
console.log(arg);
}
arga( arr1 , 26, from ); // [ arr1 ,26, from ]
映射转换
function arga(...args) {
return Array.from(args, value => value + 1);
}
let arr = arga( arr , 26, pop );
console.log(arr);//[ arr1 ,27, pop1 ]
const helper = {
diff: 1,
add(value) {
return value + this.diff;
}
}
function translate() {
//arguments 是一个对应于传递给函数的参数的类数组对象
return Array.from(arguments, helper.add, helper);
}
let arr = translate( liu , 26, man );
console.log(arr); // ["liu1", 27, "man1"]
二、数组方法
数组原型方法主要有以下这些
join():用指定的分隔符将数组每一项拼接为字符串
push() :向数组的末尾添加新元素
pop():删除数组的最后一项
shift():删除数组的第一项
unshift():向数组首位添加新元素
slice():按照条件查找出其中的部分元素
splice():对数组进行增删改
fill(): 方法能使用特定值填充数组中的一个或多个元素
filter():“过滤”功能
concat():用于连接两个或多个数组
indexOf():检测当前值在数组中第一次出现的位置索引
lastIndexOf():检测当前值在数组中最后一次出现的位置索引
every():判断数组中每一项都是否满足条件
some():判断数组中是否存在满足条件的项
includes():判断一个数组是否包含一个指定的值
sort():对数组的元素进行排序
reverse():对数组进行倒序
forEach():ES5 及以下循环遍历数组每一项
map():ES6 循环遍历数组每一项
copyWithin():用于从数组的指定位置拷贝元素到数组的另一个指定位置中
find():返回匹配的值
findIndex():返回匹配位置的索引
toLocaleString()、toString():将数组转换为字符串
flat()、flatMap():扁平化数组
entries() 、keys() 、values():遍历数组
各个方法的基本功能详解
1、join()
var arr = [1,2,3];
console.log(arr.join()); // 1,2,3
console.log(arr.join("-")); // 1-2-3
console.log(arr); // [1, 2, 3](原数组不变)
function repeatString(str, n) {
//一个长度为n+1的空数组用string去拼接成字符串,就成了n个string的重复
return new Array(n + 1).join(str);
}
console.log(repeatString("abc", 3)); // abcabcabc
console.log(repeatString("Hi", 5)); // HiHiHiHiHi
2、push()和 pop()
var arr = ["Lily","lucy","Tom"];
var count = arr.push("Jack","Sean");
console.log(count); // 5
console.log(arr); // ["Lily", "lucy", "Tom", "Jack", "Sean"]
var item = arr.pop();
console.log(item); // Sean
console.log(arr); // ["Lily", "lucy", "Tom", "Jack"]
3、shift() 和 unshift()
var arr = ["Lily","lucy","Tom"];
var count = arr.unshift("Jack","Sean");
console.log(count); // 5
console.log(arr); //["Jack", "Sean", "Lily", "lucy", "Tom"]
var item = arr.shift();
console.log(item); // Jack
console.log(arr); // ["Sean", "Lily", "lucy", "Tom"]
4、sort()
var arr1 = ["a", "d", "c", "b"];
console.log(arr1.sort()); // ["a", "b", "c", "d"]
arr2 = [13, 24, 51, 3];
console.log(arr2.sort()); // [13, 24, 3, 51]
console.log(arr2); // [13, 24, 3, 51](元数组被改变)
function compare(value1, value2) {
if (value1 < value2) {
return -1;
} else if (value1 > value2) {
return 1;
} else {
return 0;
}
}
arr2 = [13, 24, 51, 3];
console.log(arr2.sort(compare)); // [3, 13, 24, 51]
function compare(value1, value2) {
if (value1 < value2) {
return 1;
} else if (value1 > value2) {
return -1;
} else {
return 0;
}
}
arr2 = [13, 24, 51, 3];
console.log(arr2.sort(compare)); // [51, 24, 13, 3]
5、reverse()
var arr = [13, 24, 51, 3];
console.log(arr.reverse()); //[3, 51, 24, 13]
console.log(arr); //[3, 51, 24, 13](原数组改变)
6、concat()
var arr = [1,3,5,7];
var arrCopy = arr.concat(9,[11,13]);
console.log(arrCopy); //[1, 3, 5, 7, 9, 11, 13]
console.log(arr); // [1, 3, 5, 7](原数组未被修改)
var arrCopy2 = arr.concat([9,[11,13]]);
console.log(arrCopy2); //[1, 3, 5, 7, 9, Array[2]]
console.log(arrCopy2[5]); //[11, 13]
7、slice()
var arr = [1,3,5,7,9,11];
var arrCopy = arr.slice(1);
var arrCopy2 = arr.slice(1,4);
var arrCopy3 = arr.slice(1,-2);//相当于arr.slice(1,4)
var arrCopy4 = arr.slice(-4,-1);//相当于arr.slice(2,5)
console.log(arr); //[1, 3, 5, 7, 9, 11](原数组没变)
console.log(arrCopy); //[3, 5, 7, 9, 11]
console.log(arrCopy2); //[3, 5, 7]
console.log(arrCopy3); //[3, 5, 7]
console.log(arrCopy4); //[5, 7, 9]
8、splice()
var arr = [1,3,5,7,9,11];
var arrRemoved = arr.splice(0,2);
console.log(arr); //[5, 7, 9, 11]
console.log(arrRemoved); //[1, 3]
var array1 = [22, 3, 31, 12];
array1.splice(1, 0, 12, 35); //[]
console.log(array1); // [22, 12, 35, 3, 31, 12]
const array1 = [22, 3, 31, 12];
array1.splice(1, 1, 8); //[3]
console.log(array1); // [22, 8, 31, 12]
9、indexOf()和 lastIndexOf()
var arr = [1,3,5,7,7,5,3,1];
console.log(arr.indexOf(5)); //2
console.log(arr.lastIndexOf(5)); //5
console.log(arr.indexOf(5,2)); //2
console.log(arr.lastIndexOf(5,4)); //2
console.log(arr.indexOf("5")); //-1
10、forEach()
var arr = [11, 22, 33, 44, 55];
arr.forEach(function(x, index, a){
console.log(x + | + index + | + (a === arr));
});
输出为:
11|0|true
22|1|true
33|2|true
44|3|true
55|4|true
11、map()
var arr = [1, 2, 3, 4, 5];
var arr2 = arr.map(function(item){
return item*item;
});
console.log(arr2); //[1, 4, 9, 16, 25]
12、filter()
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var arr2 = arr.filter(function(x, index) {
return index % 3 === 0 || x >= 8;
});
console.log(arr2); //[1, 4, 7, 8, 9, 10]
13、fill() es6 新增
let arr = [1, 2, 3, cc , 5];
arr.fill(1);
console.log(arr);//[1,1,1,1,1];
let arr = [1, 2, 3, arr , 5];
arr.fill(1, 2);
console.log(arr);//[1,2,1,1,1]
arr.fill(0, 1, 3);
console.log(arr);//[1,0,0,1,1];
14、every()
var arr = [1, 2, 3, 4, 5];
var arr2 = arr.every(function(x) {
return x < 10;
});
console.log(arr2); //true
var arr3 = arr.every(function(x) {
return x < 3;
});
console.log(arr3); // false
15、some()
var arr = [1, 2, 3, 4, 5];
var arr2 = arr.some(function(x) {
return x < 3;
});
console.log(arr2); //true
var arr3 = arr.some(function(x) {
return x < 1;
});
console.log(arr3); // false
16、includes() es7 新增
const array1 = [22, 3, 31, 12, arr ];
const includes = array1.includes(31);
console.log(includes); // true
const includes1 = array1.includes(31, 3); // 从索引3开始查找31是否存在
console.log(includes1); // false
let values = [1, NaN, 2];
console.log(values.indexOf(NaN));//-1
console.log(values.includes(NaN));//true
17、reduce()和 reduceRight()
var values = [1,2,3,4,5];
var sum = values.reduceRight(function(prev, cur, index, array){
return prev + cur;
},10); //数组一开始加了一个初始值10,可以不设默认0
console.log(sum); //25
18、toLocaleString() 和 toString()
const array1 = [22, 3, 31, 12];
const str = array1.toLocaleString();
const str1 = array1.toString();
console.log(str); // 22,3,31,12
console.log(str1); // 22,3,31,12
19、 find()和 findIndex()
let arr = [1, 2, 3, arr , 5, 1, 9];
console.log(arr.find((value, keys, arr) => {
return value > 2;
})); // 3 返回匹配的值
console.log(arr.findIndex((value, keys, arr) => {
return value > 2;
})); // 2 返回匹配位置的索引
20、copyWithin() [es6 新增]
//将数组的前两个元素复制到数组的最后两个位置
let arr = [1, 2, 3, arr , 5];
arr.copyWithin(3, 0);
console.log(arr);//[1,2,3,1,2]
let arr = [1, 2, 3, arr , 5, 9, 17];
//从索引3的位置开始粘贴
//从索引0的位置开始复制
//遇到索引3时停止复制
arr.copyWithin(3, 0, 3);
console.log(arr);//[1,2,3,1,2,3,17]
21、flat() 和 flatMap() es6 新增
const arr1 = [0, 1, 2, [3, 4]];
console.log(arr1.flat());
// expected output: [0, 1, 2, 3, 4]
const arr2 = [0, 1, 2, [[[3, 4]]]];
console.log(arr2.flat(2));
// expected output: [0, 1, 2, [3, 4]]
//使用 Infinity,可展开任意深度的嵌套数组
var arr4 = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];
arr4.flat(Infinity);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
// 扁平化数组空项,如果原数组有空位,flat()方法会跳过空位
var arr4 = [1, 2, , 4, 5];
arr4.flat();
// [1, 2, 4, 5]
// 相当于 [[2, 4], [3, 6], [4, 8]].flat()
[2, 3, 4].flatMap((x) => [x, x * 2])
// [2, 4, 3, 6, 4, 8]
22、 entries(),keys() 和 values() 【ES6】
for (let index of [ a , b ].keys()) {
console.log(index);
}
// 0
// 1
for (let elem of [ a , b ].values()) {
console.log(elem);
}
// a
// b
for (let [index, elem] of [ a , b ].entries()) {
console.log(index, elem);
}
// 0 "a"
// 1 "b"
let letter = [ a , b , c ];
let entries = letter.entries();
console.log(entries.next().value); // [0, a ]
console.log(entries.next().value); // [1, b ]
console.log(entries.next().value); // [2, c ]
支持下