JavaScript数组知识
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<title>数组操作</title>
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/*
//instanceof
var arr = [12,23,45,6,89];
console.log(arr instanceof Array);//true
//Array.isArray(参数); // 判断参数是不是数组,返回布尔值;
var arr = [1, 2, 3];
var num = 123;
console.log(Array.isArray(arr));//true
console.log(Array.isArray(num));//false
// 数组.toString() 把数组变成字符串，去除[] 内容有逗号链接
var arr = ["aaa","bbb","ccc"];
console.log(arr.toString());// aaa,bbb,ccc
//数组.valueOf() 返回数组本身
var arr = ["aaa","bbb","ccc"];
console.log(arr.valueOf());// ["aaa", "bbb", "ccc"]
//数组.join(参数) 数组中的元素可以按照参数进行连接变成一个字符串
var arr = ["aaa","bbb","ccc"];
//console.log(arr.join("-"));// "aaa-bbb-ccc"
//console.log(arr.join(""));// "aaabbbccc"
//console.log(arr.join(" "));// "aaa bbb ccc"
//数组.push() //在数组的最末尾添加元素;
var arr = [1,2,3,4];
var arr1 = arr.push(0);
console.log(arr);//[1, 2, 3, 4, 0]
console.log(arr1);// 5 返回数组的长度
//数组.pop() 不需要参数 在数组的最末尾删除一项
var arr = [1,2,3,4];
var arr2 = arr.pop();
console.log(arr);// [1, 2, 3] 改变原数组
console.log(arr2);// 4 返回值是被删除的一项
//数组.unshift() //在数组的最前面添加一个元素;
var arr = [1,2,3,4];
var arr3 = arr.unshift(9);
console.log(arr);//[9, 1, 2, 3, 4]
console.log(arr3);//5 返回值是数组的长度
//数组.shift() 不需要参数 在数组的最前面删除一项
var arr = [1,2,3,4];
var arr4 = arr.shift();
console.log(arr);//[2, 3, 4] 返回被修改的数组
console.log(arr4);// 1 返回被删除的一项
//数组元素的排序
//reverse() 翻转数组
var arr = [12,56,89,98,68,87];
var arr5 = arr.reverse();
console.log(arr);// [87, 68, 98, 89, 56, 12]
console.log(arr5);// [87, 68, 98, 89, 56, 12]
//sort() // 数组中元素排序;(默认：从小到大)
//默认：按照首个字符的Unicode编码排序;如果第一个相同那么就比较第二个...
var arr = [12,35,24,56,42,8,5,68,86];
var arr6 = arr.sort();
console.log(arr);//[12, 24, 35, 42, 5, 56, 68, 8, 86]
console.log(arr6);//[12, 24, 35, 42, 5, 56, 68, 8, 86]
//sort() 用回调函数进行升序和降序的排列
var arr = [12,35,24,56,42,8,5,68,86];
arr.sort(function(a,b){
return a-b;//升序排列
});
console.log(arr);//[5, 8, 12, 24, 35, 42, 56, 68, 86]
//数组元素的操作
//concat()
var arr = [1,2,3];
var arr8 = ["a","b","c"];
var arr9 = arr.concat(arr8);
console.log(arr);//[1, 2, 3]
console.log(arr8);//["a", "b", "c"]
console.log(arr9); //[1, 2, 3, "a", "b", "c"]
//数组.slice(开始索引值，结束索引值);不包括结束索引 //数组截取;
var arr = [1, 2, 3, "a", "b", "c"];
var arr10 = arr.slice(1,4);
console.log(arr);//[1, 2, 3, "a", "b", "c"]
console.log(arr10);//[2, 3, "a"]
//数组.splice(开始索引值，删除几个，替换内容1，替换内容2，...);
// 替换和删除; 改变原数组;返回值是被删除/替换的内容
var arr = [1,2,3,4,5,6,'a','b','c','d','e','f'];
//var arr11 = arr.splice(5);//从索引为5开始截取到最后
//console.log(arr);//[1, 2, 3, 4, 5]
//console.log(arr11);//[6, "a", "b", "c", "d", "e", "f"]
//var arr12 = arr.splice(2,5);//从索引为2开始截取5个元素
//console.log(arr);//[1, 2, "b", "c", "d", "e", "f"]
arr.splice(6,3,"aaa","bbb","ccc");//删除并替换
console.log(arr);// [1, 2, 3, 4, 5, 6, "aaa", "bbb", "ccc", "d", "e", "f"]
//数组.indexOf(元素); // 给元素，查索引(从前往后)
// 数组.lastIndexOf(元素); // 给元素，查索引(从后往前)
var arr = ["a","b","c","d","e","f"];
console.log(arr.indexOf("e"));// 4
console.log(arr.lastIndexOf("c"));//2
*/
//数组迭代(遍历)
/*数组.every() 对数组中每一项运行回调函数，如果都返回true，every返回true，如果有一项返回false，
则停止遍历 every返回false；不写默认返回false*/
/*var arr = [1,2,3,4,5];
arr.every(function(ele,index,arr){
console.log(a);//元素
console.log(b);//索引
console.log(c);//数组本身
});*/
/*var arr = [123,234,567,768,987];
//every返回一个bool值，全部是true才是true；有一个是false，结果就是false
var bool = arr.every(function(ele,index,arr){
if(ele>100){
return true;
}else{
return false;
}
});
console.log(bool);*/
/*filter()对数组中每一项运行回调函数，该函数返回结果是true的项组成的新数组
新数组是有老数组中的元素组成的，return为ture的项;*/
/*var arr = [123,123,45,678,54,678];
var arr0 = arr.filter(function(element,index,array){
if(element>100){
return true;
}else{
return false;
}
});
console.log(arr0);//[123, 123, 678, 678]*/
//forEach() 和 for循环一样没有返回值
/*var arr = [1,2,3,4,5,6,7];
arr.forEach(function(element,index,array){
console.log(element);
console.log(index);
console.log(array);
});*/
/*map()对数组中每一项运行回调函数，返回该函数的结果组成的新数组。
return什么新数组中就有什么，不return返回undefined，对数组二次加工。*/
/*var arr = [1,2,3,4,5,6,7,8];
var newArr = arr.map(function(element,index,array){
if(index==2||index==3){
return element;
}else{
return element*2;
}
});
console.log(newArr);// [2, 4, 3, 4, 10, 12, 14, 16]*/
//some()对数组中每一项运行回调函数，如果该函数对某一项返回true，则some返回true; 像杀手，有一个成功，就胜利了！！！
/*var arr = [1,2,4,5,6,7,8,10];
var bool = arr.some(function(ele,index,array){
if(ele%3==0){
return true;
}
return false;
});
console.log(bool);*/
//数组的清空
/*1、arr.length = 0; 伪数组无法清空
* 2、arr.splice(0); 伪数组中没有该方法
* 3、arr = []; 可以操作伪数组(推荐)
* 4、伪数组：就是长的像数组，但是没有数组的方法;也不能添加和删除元素;
*
* */
//清空数组的案例
/*function test(){
//arguments.length = 0;//console.log(arguments);打印Arguments [0: 1, 1: 2, 2: 3, 3: 4, callee: ƒ, Symbol(Symbol.iterator): ƒ]
//arguments.splice(0);//console.log(arguments);//Uncaught TypeError: arguments.splice is not a function
arguments = [];//可以清空 返回空数组
console.log(arguments);
}
test(1,2,3,4);*/
//数组案例
/*
* ["刘备","张飞","关羽"] 1.将一个字符串数组输出为|分割的形式，比如“刘备|张飞|关羽”。使用两种方式实现
* */
//方法一
/*var arr = ["刘备","张飞","关羽"];
var arr1 = arr.join('|');
console.log(arr1);//"刘备|张飞|关羽"*/
//方法二
/* var arr = ["刘备","张飞","关羽"];
var separator = "|";
var str = arr[0];
for(var i = 1;i<arr.length;i++){
str += separator+arr[i];
}
console.log(str);//"刘备|张飞|关羽"*/ //["c", "a", "z", "a", "x", "a"] 输出a所在的索引
/*var arr = ["c", "a", "z", "a", "x", "a"];
arr.forEach(function(element,index,array){
if(element=="a"){
console.log(index);//1,3,5
}
});*/
/*判断特殊情况
false == "" // true
false == [] // true
false == {} // false
"" == 0 // true
"" == [] // true
"" == {} // false
0 == [] // true
0 == {} // false
0 == null // false
null == undefined // true
[]==false // true
[] == ![] // true
*/
/*var a = "0";
console.log(Boolean(a));//true
var b = false;
console.log(Boolean(b));//false
console.log(a==b);//true == 比较的是强制类型转换后的值 === 是直接比较
*/
// 数组.toString() 把数组变成字符串，去除[] 内容有逗号链接
//let arr = [1,2,3,4,5,6,7,8,9];
//console.log(arr.toString()); // '1,2,3,4,5,6,7,8,9' //数组.valueOf() 返回数组本身
//let arr = [1,2,3,4,5,6,7,8,9];
//console.log(arr.valueOf());//[1, 2, 3, 4, 5, 6, 7, 8, 9]
//数组.join(参数) 数组中的元素可以按照参数进行连接变成一个字符串
// var arr = ["aaa","bbb","ccc"];
// console.log(arr.join("-"));// 'aaa-bbb-ccc'
// console.log(arr.join(""));// 'aaabbbccc'
// console.log(arr.join(" "));// 'aaa bbb ccc'
// console.log(arr.join("~"));// 'aaa~bbb~ccc'
//sort() 用回调函数进行升序和降序的排列 箭头函数
//var arr = [12,35,24,56,42,8,5,68,86];
//升序
//arr.sort((a,b) => a-b);
//console.log(arr);//[5, 8, 12, 24, 35, 42, 56, 68, 86]
//降序
//arr.sort((a,b) => b-a);
//console.log(arr);
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