javascript的基础应用
有关网页互动基本函数
<script id = "testWeb" type="text/javascript">
window.alert("123");
window.alert("'123'");//出现两次 弹出页面提示
console.log("123");//在网页console中出现,检查控制台输出
var str = window.prompt("请输入用户名:");
console.log(str);
console.warn("警示");
</script>
有关代码的基本语法
定义数据类型
<script id = "testGrammar" type="text/javascript">
var name = "陆夏";//定义变量
name = "夏陆";//更改变量
const PI = 3.14;//定义常量
</script>
数字的使用
<script id = "testNumber" type="text/javascript">
var age = 3;
var id = 4;
window.alert(age*id);
var num = 1/0;
console.log(num);//输出Infinity
console.log(Number.MAX_SAFE_INTEGER);
console.log(Number.MAX_VALUE);//1.7976931348623157e+308
console.log(Number("456f345"))//->NaN
</script>
转换为数字
字符串转数字,使用Number()函数,如果有字母将会转成NaN,空格或空字符串转为0
var str1 = '123';
console.log(Number(str1));
var str2 = '123a';
console.log(Number(str2)); //NaN
var str3 = '';
console.log(Number(str3));//0
var str4 = ' ';
console.log(Number(str4));//0
字符串转数字,使用parseInt()函数,遇小数点和字母就截断,如果只有字母则输出NaN
var str5 = "123";
console.log(parseInt(str5));//123
var str6 = "123.5";
console.log(parseInt(str6));//123
var str7 = '123a';
console.log(Number(str7)); //123
var str8 = '123a456';
console.log(Number(str8)); //123
var str9 = '';
console.log(Number(str9));//0
var str10 = ' ';
console.log(Number(str10));//0
var str11 = 'csdn';
console.log(Number(str11));//NaN
布尔值的转换
Boolean()函数
0为false 1为true NaN为false ""为false -1等数字为true " "为true
<script id = "testBoolean" type="text/javascript">
var bool = Boolean(3);
window.alert(bool);//0为false 1为true NaN为false ""为false -1等数字为true " "为true
</script>
字符串的转换
var num = 100;
console.log(num);//数字类型的
console.log(num.toString());//数字转为字符串
console.log(typeof num.toString());//String
var num2 = 5;
console.log(String(num2));
console.log(String(null));
console.log(String(undefined));//以上均输出字符串类型的
console.log(10 + 12 + "1"); // 与字符串连接,自动类型转换为字符型
本文地址:https://blog.csdn.net/qq_46132256/article/details/109372928
您可能感兴趣的文章:
- vue init初始化项目后 npm run dev报错 10% building modules 1/1 modules 0 activeevents
- axios 处理 302 状态码的解决方法
- [Intervention] Unable to preventDefault inside passive event listener due to target being treated as passive. See https://www.chromestatus.com/feature
- react-native 在新版Xcode(10+)中运行出现的问题: node_modules/react-native/third-party/glog-0.3.4 , C compiler cannot create executables
- 使用puppeteer爬取网站并抓出404无效链接
- 【angular2+typeScript+ng-zorro】Carousel 走马灯的左右方向控件实现
如您对本文有疑问或者有任何想说的,请点击进行留言回复,万千网友为您解惑!
网友评论