极客笔记JavaScript中的switch case语句
在JavaScript中，switch case语句是一种用于多个条件判断的控制语句。它可以根据表达式的值，选择执行不同的代码块。在本文中，我们将详细介绍switch case语句的用法，并提供多个示例代码来帮助读者更好地理解。
基本语法
switch case语句的基本语法如下：
switch(expression) {
case value1:
// 当expression等于value1时执行的代码块
break;
case value2:
// 当expression等于value2时执行的代码块
break;
default:
// 当expression不等于任何case时执行的代码块
}
在上面的语法中，expression是一个表达式，可以是任何数据类型，而value1、value2等则是具体的值。当expression的值等于某个case的值时，就会执行对应的代码块。如果没有匹配的case，则会执行default代码块。
示例代码
示例1：根据星期几输出不同的提示信息
let day = 'Monday';
switch(day) {
case 'Monday':
console.log('今天是星期一');
break;
case 'Tuesday':
console.log('今天是星期二');
break;
case 'Wednesday':
console.log('今天是星期三');
break;
case 'Thursday':
console.log('今天是星期四');
break;
case 'Friday':
console.log('今天是星期五');
break;
case 'Saturday':
console.log('今天是星期六');
break;
case 'Sunday':
console.log('今天是星期日');
break;
default:
console.log('输入错误');
}
代码运行结果:
示例2：根据用户输入的数字输出对应的中文数字
let num = 3;
switch(num) {
case 1:
console.log('一');
break;
case 2:
console.log('二');
break;
case 3:
console.log('三');
break;
case 4:
console.log('四');
break;
case 5:
console.log('五');
break;
default:
console.log('输入错误');
}
代码运行结果:
示例3：根据用户输入的月份输出该月份的天数
let month = 2;
let days;
switch(month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
days = 31;
break;
case 4:
case 6:
case 9:
case 11:
days = 30;
break;
case 2:
days = 28;
break;
default:
console.log('输入错误');
}
console.log(`{month}月有{days}天`);
代码运行结果:
示例4：根据用户输入的成绩输出对应的等级
let score = 85;
let grade;
switch(true) {
case score >= 90:
grade = '优秀';
break;
case score >= 80:
grade = '良好';
break;
case score >= 70:
grade = '中等';
break;
case score >= 60:
grade = '及格';
break;
default:
grade = '不及格';
}
console.log(`成绩为{score}，等级为{grade}`);
代码运行结果:
示例5：根据用户输入的运算符进行计算
let num1 = 10;
let num2 = 5;
let operator = '+';
let result;
switch(operator) {
case '+':
result = num1 + num2;
break;
case '-':
result = num1 - num2;
break;
case '*':
result = num1 * num2;
break;
case '/':
result = num1 / num2;
break;
default:
console.log('运算符错误');
}
console.log(`{num1}{operator} {num2} ={result}`);
代码运行结果:
示例6：根据用户输入的颜色输出对应的RGB值
let color = 'red';
let rgb;
switch(color) {
case 'red':
rgb = '255, 0, 0';
break;
case 'green':
rgb = '0, 255, 0';
break;
case 'blue':
rgb = '0, 0, 255';
break;
default:
console.log('颜色错误');
}
console.log(`{color}的RGB值为({rgb})`);
代码运行结果:
示例7：根据用户输入的季节输出对应的活动
let season = 'summer';
let activity;
switch(season) {
case 'spring':
activity = '踏青';
break;
case 'summer':
activity = '游泳';
break;
case 'autumn':
activity = '采摘';
break;
case 'winter':
activity = '滑雪';
break;
default:
console.log('季节错误');
}
console.log(`现在是{season}，适合{activity}`);
代码运行结果:
示例8：根据用户输入的星座输出对应的特点
let constellation = '双子座';
let trait;
switch(constellation) {
case '白羊座':
trait = '热情';
break;
case '金牛座':
trait = '稳重';
break;
case '双子座':
trait = '聪明';
break;
case '巨蟹座':
trait = '细腻';
break;
default:
console.log('星座错误');
}
console.log(`{constellation}的特点是{trait}`);
代码运行结果:
示例9：根据用户输入的城市输出对应的天气
let city = '北京';
let weather;
switch(city) {
case '北京':
weather = '晴';
break;
case '上海':
weather = '阴';
break;
case '广州':
weather = '雨';
break;
case '成都':
weather = '雪';
break;
default:
console.log('城市错误');
}
console.log(`{city}的天气是{weather}`);
代码运行结果:
示例10：根据用户输入的水果输出对应的颜色
let fruit = 'apple';
let color;
switch(fruit) {
case 'apple':
color = 'red';
break;
case 'banana':
color = 'yellow';
break;
case 'orange':
color = 'orange';
break;
case 'grape':
color = 'purple';
break;
default:
console.log('水果错误');
}
console.log(`{fruit}的颜色是{color}`);
代码运行结果:
示例11：根据用户输入的动物输出对应的叫声
let animal = 'cat';
let sound;
switch(animal) {
case 'cat':
sound = '喵喵';
break;
case 'dog':
sound = '汪汪';
break;
case 'cow':
sound = '哞哞';
break;
case 'duck':
sound = '嘎嘎';
break;
default:
console.log('动物错误');
}
console.log(`{animal}的叫声是{sound}`);
代码运行结果:
示例12：根据用户输入的汽车品牌输出对应的国家
let carBrand = 'Toyota';
let country;
switch(carBrand) {
case 'Toyota':
case 'Honda':
case 'Nissan':
country = 'Japan';
break;
case 'BMW':
case 'Mercedes':
case 'Volkswagen':
country = 'Germany';
break;
case 'Ford':
case 'Chevrolet':
country = 'USA';
break;
default:
console.log('品牌错误');
}
console.log(`{carBrand}的产地是{country}`);
代码运行结果:
示例13：根据用户输入的电影类型输出对应的经典电影
let genre = 'comedy';
let movie;
switch(genre) {
case 'action':
movie = 'The Dark Knight';
break;
case 'comedy':
movie = 'Home Alone';
break;
case 'drama':
movie = 'The Shawshank Redemption';
break;
case 'horror':
movie = 'The Exorcist';
break;
default:
console.log('类型错误');
}
console.log(`{genre}类型的经典电影是{movie}`);
代码运行结果:
示例14：根据用户输入的食物输出对应的国家
let food = 'sushi';
let country;
switch(food) {
case 'sushi':
country = 'Japan';
break;
case 'pizza':
country = 'Italy';
break;
case 'taco':
country = 'Mexico';
break;
case 'croissant':
country = 'France';
break;
default:
console.log('食物错误');
}
console.log(`{food}的产地是{country}`);
代码运行结果:
示例15：根据用户输入的衣服颜色输出对应的搭配建议
let clothesColor = 'blue';
let suggestion;
switch(clothesColor) {
case 'red':
suggestion = '搭配白色裤子';
break;
case 'blue':
suggestion = '搭配黑色鞋子';
break;
case 'green':
suggestion = '搭配灰色围巾';
break;
case 'yellow':
suggestion = '搭配蓝色帽子';
break;
default:
console.log('颜色错误');
}
console.log(`穿{clothesColor}衣服时，{suggestion}`);
代码运行结果:
示例16：根据用户输入的节日输出对应的传统食物
let holiday = 'Christmas';
let food;
switch(holiday) {
case 'Christmas':
food = 'Roast turkey';
break;
case 'Lunar New Year':
food = 'Dumplings';
break;
case 'Thanksgiving':
food = 'Pumpkin pie';
break;
case 'Easter':
food = 'Hot cross buns';
break;
default:
console.log('节日错误');
}
console.log(`{holiday}节日的传统食物是{food}`);
代码运行结果:
示例17：根据用户输入的音乐风格输出对应的代表歌手
let musicStyle = 'pop';
let singer;
switch(musicStyle) {
case 'pop':
singer = 'Taylor Swift';
break;
case 'rock':
singer = 'Queen';
break;
case 'hip hop':
singer = 'Eminem';
break;
case 'country':
singer = 'Dolly Parton';
break;
default:
console.log('音乐风格错误');
}
console.log(`{musicStyle}音乐风格的代表歌手是{singer}`);
代码运行结果:
示例18：根据用户输入的运动项目输出对应的比赛规则
let sport = 'football';
let rules;
switch(sport) {
case 'football':
rules = '11 players per team';
break;
case 'basketball':
rules = '5 players per team';
break;
case 'tennis':
rules = 'singles or doubles';
break;
case 'swimming':
rules = 'different strokes';
break;
default:
console.log('运动项目错误');
}
console.log(`{sport}比赛的规则是{rules}`);
代码运行结果:
示例19：根据用户输入的书籍类型输出对应的经典作品
let bookType = 'science fiction';
let classicBook;
switch(bookType) {
case 'science fiction':
classicBook = '1984 by George Orwell';
break;
case 'romance':
classicBook = 'Pride and Prejudice by Jane Austen';
break;
case 'mystery':
classicBook = 'Sherlock Holmes by Arthur Conan Doyle';
break;
case 'fantasy':
classicBook = 'The Lord of the Rings by J.R.R. Tolkien';
break;
default:
console.log('书籍类型错误');
}
console.log(`{bookType}类型的经典作品是{classicBook}`);
代码运行结果:
示例20：根据用户输入的城市输出对应的地标
let landmark;
let city = 'Paris';
switch(city) {
case 'Paris':
landmark = 'Eiffel Tower';
break;
case 'New York':
landmark = 'Statue of Liberty';
break;
case 'Beijing':
landmark = 'Great Wall of China';
break;
case 'Sydney':
landmark = 'Sydney Opera House';
break;
default:
console.log('城市错误');
}
console.log(`{city}的地标是{landmark}`);
代码运行结果:
以上是关于JavaScript中switch case语句的详细介绍和示例代码。通过这些示例，读者可以更深入理解switch case语句的用法和灵活性，灵活运用switch case语句可以根据不同的条件执行不同的代码块，使代码更加清晰和易于维护。