JS篇 ⑨
01 数组①
定义
一个包含了多个值的对象通常被描述为“像列表一样的对象”一组数据的集合，存储在单个变量名下的优雅方式
创建数组
利用new创建数组：var arr = new Array();利用数组字面量创建数组：var arr = [];数组里面的数据一定用逗号分隔，如：var arr1 = [1, 2, "hello", true];
获取数组元素
数组元素：数组里面的数据*数组名[索引号]*，索引号从0开始vararr1= [1, 2, "hello", true];console.log(arr1[3]); // trueconsole.log(arr1[4]); // 由于没有这个数组元素 所以输出的结果是 undefined
数组长度
数组名.length数组的长度是元素个数，不要跟索引号搅浑vararr1= [1, 2, "hello", true];console.log(arr1.length); // 4
遍历数组
把数组的元素从头到尾访问一次vararr= ["red", "green", "blue"];for (vari=; i<3; i++) {console.log(arr[i]); // red, green, blue}由于数组索引号从0开始，所以 i 必需从0开始
02 数组②
检测是否为数组
变量名 instanceof ArrayArray.isArray(变量名)
案例：求数组[2,6,1,77,52,25,7]中的最大值vararr= [2, 6, 1, 77, 52, 25, 7, 99];varmax=arr[];for (vari=1; i<arr.length; i++) {if (arr[i] >max) {max=arr[i]; }}console.log(max); // 99
数组转为字符串案例：将数组 ["red", "green", "blue", "pink"] 转换为字符串，并且用 | 或其他符号分割
遍历，将每个数据分别拿出来，后面加分隔符vararr= ["red", "green", "blue", "pink"];varstr="";varsep="|";for (vari=; i<arr.length-1; i++) {str+=arr[i] +sep;}str+=arr[arr.length-1];console.log(str);arr.join(分隔符)vararr= ["red", "green", "blue", "pink"];console.log(arr.join("|"));
新增数组元素
直接修改数组长度：多于原来的长度，多出的数，值为undefined；少于原来的长度，按索引号顺序将后面的去掉vararr= ["red", "green", "blue"];console.log(arr.length);arr.length=5;console.log(arr); // ["red", "green", "blue", , ]console.log(arr[3]); // undefined修改索引号：arr[index] = 值vararr1= ["red", "green", "blue"];arr1[3] ="yellow";console.log(arr1.length); // 4console.log(arr1); // ["red", "green", "blue", "yellow"]console.log(arr1[3]); // yellow
添加删除数组元素
push()：数组末尾添加一或多个元素vararr1= ["red", "green", "blue"];arr1.push("yellow");console.log(arr1); // [ "red", "green", "blue", "yellow" ]pop()：删除数组最后一个元素vararr1= ["red", "green", "blue"];arr1.pop();console.log(arr1); // [ "red", "green" ]unshift()：数组开头添加一或多个元素vararr1= ["red", "green", "blue"];arr1.unshift("yellow");console.log(arr1); // [ "yellow", "red", "green", "blue" ]shift()：删除数组开头一个元素vararr1= ["red", "green", "blue"];arr1.shift();console.log(arr1); // [ "green", "blue" ]
03 数组③
获取数组元素索引
第二个参数默认为，从头开始查找。若设置参数，则从该参数所显示的索引号开始查找
arr.indexOf(前提)：返回满足条件的第一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.indexOf("red")); // 0arr.lastIndexOf(前提)：返回满足条件的最后一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.lastIndexOf("red")); // 4
筛选数组案例：将数组 [2, 0, 6, 1, 77, 0, 52, 0, 25, 7] 中大于即是 10 的元素选出来，放入新数组
方法一：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];varj=;for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[j] =arr[i];j++; }}console.log(newArr); // [77, 52, 25]方法二：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];// 刚开始 newArr.length 就是 0for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[newArr.length] =arr[i]; }}console.log(newArr); // [77, 52, 25]
数组去重案例：将数组[2, 0, 6, 1, 77, 0, 52, 0, 25, 7]中的 重复的元素 去掉后，形成一个不重复的新数组vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];for (vari=; i<arr.length; i++) {for (varj=; j<arr.length; j++) {if (newArr.indexOf(arr[i]) ==-1) {newArr.push(arr[i]); } }}console.log(newArr); // [2, 0, 6, 1, 77, 52, 25, 7]
翻转数组案例：将数组 ["red", "green", "blue", "pink", "purple"] 的内容反过来存放
遍历vararr= ["red", "green", "blue", "purple", "hotpink"];varnewArr= [];for (vari=arr.length-1; i>=; i--) {newArr[newArr.length] =arr[i]}console.log(newArr); // ["hotpink", "purple", "blue", "green", "red"]arr.reverse()vararr= ["red", "green", "blue", "purple", "hotpink"];console.log(arr.reverse()); // ["hotpink", "purple", "blue", "green", "red"]
冒泡排序
第一个数和第二个数进行比较，顺序不对则交换交换后的第二个数和第三个数进行比较...一遍后，最后的那个数不是最大就是最小然后进行第二遍，直到获取准确顺序vararr= [4, 1, 2, 3, 5];for (vari=; i<=arr.length-1; i++) { // 外层轮回管趟数 for (varj=; j<=arr.length-i-1; j++) { // 里面的轮回管 每一趟的交换次数// 内部交换2个变量的值 前一个和后面一个数组元素相比较if (arr[j] >arr[j+1]) {vartemp=arr[j];arr[j] =arr[j+1];arr[j+1] =temp; } }}console.log(arr);
交换两个变量值
方式四：利用数组②vara="111", b="222";a= [a, b];b=a[];a=a[1];console.log(a); // 222console.log(b); //111方式三：利用数组①vara="111", b="222";[a, b] = [b, a];console.log(a); // 222console.log(b); // 111
JS篇 ⑨
01 数组①
定义
一个包含了多个值的对象通常被描述为“像列表一样的对象”一组数据的集合，存储在单个变量名下的优雅方式
创建数组
利用new创建数组：var arr = new Array();利用数组字面量创建数组：var arr = [];数组里面的数据一定用逗号分隔，如：var arr1 = [1, 2, "hello", true];
获取数组元素
数组元素：数组里面的数据*数组名[索引号]*，索引号从0开始vararr1= [1, 2, "hello", true];console.log(arr1[3]); // trueconsole.log(arr1[4]); // 由于没有这个数组元素 所以输出的结果是 undefined
数组长度
数组名.length数组的长度是元素个数，不要跟索引号搅浑vararr1= [1, 2, "hello", true];console.log(arr1.length); // 4
遍历数组
把数组的元素从头到尾访问一次vararr= ["red", "green", "blue"];for (vari=; i<3; i++) {console.log(arr[i]); // red, green, blue}由于数组索引号从0开始，所以 i 必需从0开始
02 数组②
检测是否为数组
变量名 instanceof ArrayArray.isArray(变量名)
案例：求数组[2,6,1,77,52,25,7]中的最大值vararr= [2, 6, 1, 77, 52, 25, 7, 99];varmax=arr[];for (vari=1; i<arr.length; i++) {if (arr[i] >max) {max=arr[i]; }}console.log(max); // 99
数组转为字符串案例：将数组 ["red", "green", "blue", "pink"] 转换为字符串，并且用 | 或其他符号分割
遍历，将每个数据分别拿出来，后面加分隔符vararr= ["red", "green", "blue", "pink"];varstr="";varsep="|";for (vari=; i<arr.length-1; i++) {str+=arr[i] +sep;}str+=arr[arr.length-1];console.log(str);arr.join(分隔符)vararr= ["red", "green", "blue", "pink"];console.log(arr.join("|"));
新增数组元素
直接修改数组长度：多于原来的长度，多出的数，值为undefined；少于原来的长度，按索引号顺序将后面的去掉vararr= ["red", "green", "blue"];console.log(arr.length);arr.length=5;console.log(arr); // ["red", "green", "blue", , ]console.log(arr[3]); // undefined修改索引号：arr[index] = 值vararr1= ["red", "green", "blue"];arr1[3] ="yellow";console.log(arr1.length); // 4console.log(arr1); // ["red", "green", "blue", "yellow"]console.log(arr1[3]); // yellow
添加删除数组元素
push()：数组末尾添加一或多个元素vararr1= ["red", "green", "blue"];arr1.push("yellow");console.log(arr1); // [ "red", "green", "blue", "yellow" ]pop()：删除数组最后一个元素vararr1= ["red", "green", "blue"];arr1.pop();console.log(arr1); // [ "red", "green" ]unshift()：数组开头添加一或多个元素vararr1= ["red", "green", "blue"];arr1.unshift("yellow");console.log(arr1); // [ "yellow", "red", "green", "blue" ]shift()：删除数组开头一个元素vararr1= ["red", "green", "blue"];arr1.shift();console.log(arr1); // [ "green", "blue" ]
03 数组③
获取数组元素索引
第二个参数默认为，从头开始查找。若设置参数，则从该参数所显示的索引号开始查找
arr.indexOf(前提)：返回满足条件的第一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.indexOf("red")); // 0arr.lastIndexOf(前提)：返回满足条件的最后一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.lastIndexOf("red")); // 4
筛选数组案例：将数组 [2, 0, 6, 1, 77, 0, 52, 0, 25, 7] 中大于即是 10 的元素选出来，放入新数组
方法一：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];varj=;for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[j] =arr[i];j++; }}console.log(newArr); // [77, 52, 25]方法二：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];// 刚开始 newArr.length 就是 0for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[newArr.length] =arr[i]; }}console.log(newArr); // [77, 52, 25]
数组去重案例：将数组[2, 0, 6, 1, 77, 0, 52, 0, 25, 7]中的 重复的元素 去掉后，形成一个不重复的新数组vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];for (vari=; i<arr.length; i++) {for (varj=; j<arr.length; j++) {if (newArr.indexOf(arr[i]) ==-1) {newArr.push(arr[i]); } }}console.log(newArr); // [2, 0, 6, 1, 77, 52, 25, 7]
翻转数组案例：将数组 ["red", "green", "blue", "pink", "purple"] 的内容反过来存放
遍历vararr= ["red", "green", "blue", "purple", "hotpink"];varnewArr= [];for (vari=arr.length-1; i>=; i--) {newArr[newArr.length] =arr[i]}console.log(newArr); // ["hotpink", "purple", "blue", "green", "red"]arr.reverse()vararr= ["red", "green", "blue", "purple", "hotpink"];console.log(arr.reverse()); // ["hotpink", "purple", "blue", "green", "red"]
冒泡排序
第一个数和第二个数进行比较，顺序不对则交换交换后的第二个数和第三个数进行比较...一遍后，最后的那个数不是最大就是最小然后进行第二遍，直到获取准确顺序vararr= [4, 1, 2, 3, 5];for (vari=; i<=arr.length-1; i++) { // 外层轮回管趟数 for (varj=; j<=arr.length-i-1; j++) { // 里面的轮回管 每一趟的交换次数// 内部交换2个变量的值 前一个和后面一个数组元素相比较if (arr[j] >arr[j+1]) {vartemp=arr[j];arr[j] =arr[j+1];arr[j+1] =temp; } }}console.log(arr);
交换两个变量值
方式四：利用数组②vara="111", b="222";a= [a, b];b=a[];a=a[1];console.log(a); // 222console.log(b); //111方式三：利用数组①vara="111", b="222";[a, b] = [b, a];console.log(a); // 222console.log(b); // 111
JS篇 ⑨
01 数组①
定义
一个包含了多个值的对象通常被描述为“像列表一样的对象”一组数据的集合，存储在单个变量名下的优雅方式
创建数组
利用new创建数组：var arr = new Array();利用数组字面量创建数组：var arr = [];数组里面的数据一定用逗号分隔，如：var arr1 = [1, 2, "hello", true];
获取数组元素
数组元素：数组里面的数据*数组名[索引号]*，索引号从0开始vararr1= [1, 2, "hello", true];console.log(arr1[3]); // trueconsole.log(arr1[4]); // 由于没有这个数组元素 所以输出的结果是 undefined
数组长度
数组名.length数组的长度是元素个数，不要跟索引号搅浑vararr1= [1, 2, "hello", true];console.log(arr1.length); // 4
遍历数组
把数组的元素从头到尾访问一次vararr= ["red", "green", "blue"];for (vari=; i<3; i++) {console.log(arr[i]); // red, green, blue}由于数组索引号从0开始，所以 i 必需从0开始
02 数组②
检测是否为数组
变量名 instanceof ArrayArray.isArray(变量名)
案例：求数组[2,6,1,77,52,25,7]中的最大值vararr= [2, 6, 1, 77, 52, 25, 7, 99];varmax=arr[];for (vari=1; i<arr.length; i++) {if (arr[i] >max) {max=arr[i]; }}console.log(max); // 99
数组转为字符串案例：将数组 ["red", "green", "blue", "pink"] 转换为字符串，并且用 | 或其他符号分割
遍历，将每个数据分别拿出来，后面加分隔符vararr= ["red", "green", "blue", "pink"];varstr="";varsep="|";for (vari=; i<arr.length-1; i++) {str+=arr[i] +sep;}str+=arr[arr.length-1];console.log(str);arr.join(分隔符)vararr= ["red", "green", "blue", "pink"];console.log(arr.join("|"));
新增数组元素
直接修改数组长度：多于原来的长度，多出的数，值为undefined；少于原来的长度，按索引号顺序将后面的去掉vararr= ["red", "green", "blue"];console.log(arr.length);arr.length=5;console.log(arr); // ["red", "green", "blue", , ]console.log(arr[3]); // undefined修改索引号：arr[index] = 值vararr1= ["red", "green", "blue"];arr1[3] ="yellow";console.log(arr1.length); // 4console.log(arr1); // ["red", "green", "blue", "yellow"]console.log(arr1[3]); // yellow
添加删除数组元素
push()：数组末尾添加一或多个元素vararr1= ["red", "green", "blue"];arr1.push("yellow");console.log(arr1); // [ "red", "green", "blue", "yellow" ]pop()：删除数组最后一个元素vararr1= ["red", "green", "blue"];arr1.pop();console.log(arr1); // [ "red", "green" ]unshift()：数组开头添加一或多个元素vararr1= ["red", "green", "blue"];arr1.unshift("yellow");console.log(arr1); // [ "yellow", "red", "green", "blue" ]shift()：删除数组开头一个元素vararr1= ["red", "green", "blue"];arr1.shift();console.log(arr1); // [ "green", "blue" ]
03 数组③
获取数组元素索引
第二个参数默认为，从头开始查找。若设置参数，则从该参数所显示的索引号开始查找
arr.indexOf(前提)：返回满足条件的第一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.indexOf("red")); // 0arr.lastIndexOf(前提)：返回满足条件的最后一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.lastIndexOf("red")); // 4
筛选数组案例：将数组 [2, 0, 6, 1, 77, 0, 52, 0, 25, 7] 中大于即是 10 的元素选出来，放入新数组
方法一：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];varj=;for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[j] =arr[i];j++; }}console.log(newArr); // [77, 52, 25]方法二：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];// 刚开始 newArr.length 就是 0for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[newArr.length] =arr[i]; }}console.log(newArr); // [77, 52, 25]
数组去重案例：将数组[2, 0, 6, 1, 77, 0, 52, 0, 25, 7]中的 重复的元素 去掉后，形成一个不重复的新数组vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];for (vari=; i<arr.length; i++) {for (varj=; j<arr.length; j++) {if (newArr.indexOf(arr[i]) ==-1) {newArr.push(arr[i]); } }}console.log(newArr); // [2, 0, 6, 1, 77, 52, 25, 7]
翻转数组案例：将数组 ["red", "green", "blue", "pink", "purple"] 的内容反过来存放
遍历vararr= ["red", "green", "blue", "purple", "hotpink"];varnewArr= [];for (vari=arr.length-1; i>=; i--) {newArr[newArr.length] =arr[i]}console.log(newArr); // ["hotpink", "purple", "blue", "green", "red"]arr.reverse()vararr= ["red", "green", "blue", "purple", "hotpink"];console.log(arr.reverse()); // ["hotpink", "purple", "blue", "green", "red"]
冒泡排序
第一个数和第二个数进行比较，顺序不对则交换交换后的第二个数和第三个数进行比较...一遍后，最后的那个数不是最大就是最小然后进行第二遍，直到获取准确顺序vararr= [4, 1, 2, 3, 5];for (vari=; i<=arr.length-1; i++) { // 外层轮回管趟数 for (varj=; j<=arr.length-i-1; j++) { // 里面的轮回管 每一趟的交换次数// 内部交换2个变量的值 前一个和后面一个数组元素相比较if (arr[j] >arr[j+1]) {vartemp=arr[j];arr[j] =arr[j+1];arr[j+1] =temp; } }}console.log(arr);
交换两个变量值
方式四：利用数组②vara="111", b="222";a= [a, b];b=a[];a=a[1];console.log(a); // 222console.log(b); //111方式三：利用数组①vara="111", b="222";[a, b] = [b, a];console.log(a); // 222console.log(b); // 111
JS篇 ⑨
01 数组①
定义
一个包含了多个值的对象通常被描述为“像列表一样的对象”一组数据的集合，存储在单个变量名下的优雅方式
创建数组
利用new创建数组：var arr = new Array();利用数组字面量创建数组：var arr = [];数组里面的数据一定用逗号分隔，如：var arr1 = [1, 2, "hello", true];
获取数组元素
数组元素：数组里面的数据*数组名[索引号]*，索引号从0开始vararr1= [1, 2, "hello", true];console.log(arr1[3]); // trueconsole.log(arr1[4]); // 由于没有这个数组元素 所以输出的结果是 undefined
数组长度
数组名.length数组的长度是元素个数，不要跟索引号搅浑vararr1= [1, 2, "hello", true];console.log(arr1.length); // 4
遍历数组
把数组的元素从头到尾访问一次vararr= ["red", "green", "blue"];for (vari=; i<3; i++) {console.log(arr[i]); // red, green, blue}由于数组索引号从0开始，所以 i 必需从0开始
02 数组②
检测是否为数组
变量名 instanceof ArrayArray.isArray(变量名)
案例：求数组[2,6,1,77,52,25,7]中的最大值vararr= [2, 6, 1, 77, 52, 25, 7, 99];varmax=arr[];for (vari=1; i<arr.length; i++) {if (arr[i] >max) {max=arr[i]; }}console.log(max); // 99
数组转为字符串案例：将数组 ["red", "green", "blue", "pink"] 转换为字符串，并且用 | 或其他符号分割
遍历，将每个数据分别拿出来，后面加分隔符vararr= ["red", "green", "blue", "pink"];varstr="";varsep="|";for (vari=; i<arr.length-1; i++) {str+=arr[i] +sep;}str+=arr[arr.length-1];console.log(str);arr.join(分隔符)vararr= ["red", "green", "blue", "pink"];console.log(arr.join("|"));
新增数组元素
直接修改数组长度：多于原来的长度，多出的数，值为undefined；少于原来的长度，按索引号顺序将后面的去掉vararr= ["red", "green", "blue"];console.log(arr.length);arr.length=5;console.log(arr); // ["red", "green", "blue", , ]console.log(arr[3]); // undefined修改索引号：arr[index] = 值vararr1= ["red", "green", "blue"];arr1[3] ="yellow";console.log(arr1.length); // 4console.log(arr1); // ["red", "green", "blue", "yellow"]console.log(arr1[3]); // yellow
添加删除数组元素
push()：数组末尾添加一或多个元素vararr1= ["red", "green", "blue"];arr1.push("yellow");console.log(arr1); // [ "red", "green", "blue", "yellow" ]pop()：删除数组最后一个元素vararr1= ["red", "green", "blue"];arr1.pop();console.log(arr1); // [ "red", "green" ]unshift()：数组开头添加一或多个元素vararr1= ["red", "green", "blue"];arr1.unshift("yellow");console.log(arr1); // [ "yellow", "red", "green", "blue" ]shift()：删除数组开头一个元素vararr1= ["red", "green", "blue"];arr1.shift();console.log(arr1); // [ "green", "blue" ]
03 数组③
获取数组元素索引
第二个参数默认为，从头开始查找。若设置参数，则从该参数所显示的索引号开始查找
arr.indexOf(前提)：返回满足条件的第一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.indexOf("red")); // 0arr.lastIndexOf(前提)：返回满足条件的最后一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.lastIndexOf("red")); // 4
筛选数组案例：将数组 [2, 0, 6, 1, 77, 0, 52, 0, 25, 7] 中大于即是 10 的元素选出来，放入新数组
方法一：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];varj=;for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[j] =arr[i];j++; }}console.log(newArr); // [77, 52, 25]方法二：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];// 刚开始 newArr.length 就是 0for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[newArr.length] =arr[i]; }}console.log(newArr); // [77, 52, 25]
数组去重案例：将数组[2, 0, 6, 1, 77, 0, 52, 0, 25, 7]中的 重复的元素 去掉后，形成一个不重复的新数组vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];for (vari=; i<arr.length; i++) {for (varj=; j<arr.length; j++) {if (newArr.indexOf(arr[i]) ==-1) {newArr.push(arr[i]); } }}console.log(newArr); // [2, 0, 6, 1, 77, 52, 25, 7]
翻转数组案例：将数组 ["red", "green", "blue", "pink", "purple"] 的内容反过来存放
遍历vararr= ["red", "green", "blue", "purple", "hotpink"];varnewArr= [];for (vari=arr.length-1; i>=; i--) {newArr[newArr.length] =arr[i]}console.log(newArr); // ["hotpink", "purple", "blue", "green", "red"]arr.reverse()vararr= ["red", "green", "blue", "purple", "hotpink"];console.log(arr.reverse()); // ["hotpink", "purple", "blue", "green", "red"]
冒泡排序
第一个数和第二个数进行比较，顺序不对则交换交换后的第二个数和第三个数进行比较...一遍后，最后的那个数不是最大就是最小然后进行第二遍，直到获取准确顺序vararr= [4, 1, 2, 3, 5];for (vari=; i<=arr.length-1; i++) { // 外层轮回管趟数 for (varj=; j<=arr.length-i-1; j++) { // 里面的轮回管 每一趟的交换次数// 内部交换2个变量的值 前一个和后面一个数组元素相比较if (arr[j] >arr[j+1]) {vartemp=arr[j];arr[j] =arr[j+1];arr[j+1] =temp; } }}console.log(arr);
交换两个变量值
方式四：利用数组②vara="111", b="222";a= [a, b];b=a[];a=a[1];console.log(a); // 222console.log(b); //111方式三：利用数组①vara="111", b="222";[a, b] = [b, a];console.log(a); // 222console.log(b); // 111
JS篇 ⑨
01 数组①
定义
一个包含了多个值的对象通常被描述为“像列表一样的对象”一组数据的集合，存储在单个变量名下的优雅方式
创建数组
利用new创建数组：var arr = new Array();利用数组字面量创建数组：var arr = [];数组里面的数据一定用逗号分隔，如：var arr1 = [1, 2, "hello", true];
获取数组元素
数组元素：数组里面的数据*数组名[索引号]*，索引号从0开始vararr1= [1, 2, "hello", true];console.log(arr1[3]); // trueconsole.log(arr1[4]); // 由于没有这个数组元素 所以输出的结果是 undefined
数组长度
数组名.length数组的长度是元素个数，不要跟索引号搅浑vararr1= [1, 2, "hello", true];console.log(arr1.length); // 4
遍历数组
把数组的元素从头到尾访问一次vararr= ["red", "green", "blue"];for (vari=; i<3; i++) {console.log(arr[i]); // red, green, blue}由于数组索引号从0开始，所以 i 必需从0开始
02 数组②
检测是否为数组
变量名 instanceof ArrayArray.isArray(变量名)
案例：求数组[2,6,1,77,52,25,7]中的最大值vararr= [2, 6, 1, 77, 52, 25, 7, 99];varmax=arr[];for (vari=1; i<arr.length; i++) {if (arr[i] >max) {max=arr[i]; }}console.log(max); // 99
数组转为字符串案例：将数组 ["red", "green", "blue", "pink"] 转换为字符串，并且用 | 或其他符号分割
遍历，将每个数据分别拿出来，后面加分隔符vararr= ["red", "green", "blue", "pink"];varstr="";varsep="|";for (vari=; i<arr.length-1; i++) {str+=arr[i] +sep;}str+=arr[arr.length-1];console.log(str);arr.join(分隔符)vararr= ["red", "green", "blue", "pink"];console.log(arr.join("|"));
新增数组元素
直接修改数组长度：多于原来的长度，多出的数，值为undefined；少于原来的长度，按索引号顺序将后面的去掉vararr= ["red", "green", "blue"];console.log(arr.length);arr.length=5;console.log(arr); // ["red", "green", "blue", , ]console.log(arr[3]); // undefined修改索引号：arr[index] = 值vararr1= ["red", "green", "blue"];arr1[3] ="yellow";console.log(arr1.length); // 4console.log(arr1); // ["red", "green", "blue", "yellow"]console.log(arr1[3]); // yellow
添加删除数组元素
push()：数组末尾添加一或多个元素vararr1= ["red", "green", "blue"];arr1.push("yellow");console.log(arr1); // [ "red", "green", "blue", "yellow" ]pop()：删除数组最后一个元素vararr1= ["red", "green", "blue"];arr1.pop();console.log(arr1); // [ "red", "green" ]unshift()：数组开头添加一或多个元素vararr1= ["red", "green", "blue"];arr1.unshift("yellow");console.log(arr1); // [ "yellow", "red", "green", "blue" ]shift()：删除数组开头一个元素vararr1= ["red", "green", "blue"];arr1.shift();console.log(arr1); // [ "green", "blue" ]
03 数组③
获取数组元素索引
第二个参数默认为，从头开始查找。若设置参数，则从该参数所显示的索引号开始查找
arr.indexOf(前提)：返回满足条件的第一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.indexOf("red")); // 0arr.lastIndexOf(前提)：返回满足条件的最后一个索引号vararr= ["red", "green", "blue", "green", "red"];console.log(arr.lastIndexOf("red")); // 4
筛选数组案例：将数组 [2, 0, 6, 1, 77, 0, 52, 0, 25, 7] 中大于即是 10 的元素选出来，放入新数组
方法一：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];varj=;for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[j] =arr[i];j++; }}console.log(newArr); // [77, 52, 25]方法二：vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];// 刚开始 newArr.length 就是 0for (vari=; i<arr.length; i++) {if (arr[i] >=10) {// 新数组索引号应该从0开始 依次递增newArr[newArr.length] =arr[i]; }}console.log(newArr); // [77, 52, 25]
数组去重案例：将数组[2, 0, 6, 1, 77, 0, 52, 0, 25, 7]中的 重复的元素 去掉后，形成一个不重复的新数组vararr= [2, , 6, 1, 77, , 52, , 25, 7];varnewArr= [];for (vari=; i<arr.length; i++) {for (varj=; j<arr.length; j++) {if (newArr.indexOf(arr[i]) ==-1) {newArr.push(arr[i]); } }}console.log(newArr); // [2, 0, 6, 1, 77, 52, 25, 7]
翻转数组案例：将数组 ["red", "green", "blue", "pink", "purple"] 的内容反过来存放
遍历vararr= ["red", "green", "blue", "purple", "hotpink"];varnewArr= [];for (vari=arr.length-1; i>=; i--) {newArr[newArr.length] =arr[i]}console.log(newArr); // ["hotpink", "purple", "blue", "green", "red"]arr.reverse()vararr= ["red", "green", "blue", "purple", "hotpink"];console.log(arr.reverse()); // ["hotpink", "purple", "blue", "green", "red"]
冒泡排序
第一个数和第二个数进行比较，顺序不对则交换交换后的第二个数和第三个数进行比较...一遍后，最后的那个数不是最大就是最小然后进行第二遍，直到获取准确顺序vararr= [4, 1, 2, 3, 5];for (vari=; i<=arr.length-1; i++) { // 外层轮回管趟数 for (varj=; j<=arr.length-i-1; j++) { // 里面的轮回管 每一趟的交换次数// 内部交换2个变量的值 前一个和后面一个数组元素相比较if (arr[j] >arr[j+1]) {vartemp=arr[j];arr[j] =arr[j+1];arr[j+1] =temp; } }}console.log(arr);
交换两个变量值
方式四：利用数组②vara="111", b="222";a= [a, b];b=a[];a=a[1];console.log(a); // 222console.log(b); //111方式三：利用数组①vara="111", b="222";[a, b] = [b, a];console.log(a); // 222console.log(b); // 111
