3.2typeof 类型转换

最新推荐文章于 2024-06-21 12:06:26 发布

qq_49295769

最新推荐文章于 2024-06-21 12:06:26 发布

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文章标签： javascript

本文链接：https://blog.youkuaiyun.com/qq_49295769/article/details/107302330

版权

本文深入探讨了JavaScript中的各种控制流程语句，包括switch、while、for循环及continue和break的使用，并详解了类型转换的多种方式，如Number、String、Boolean等函数的运用，以及隐式类型转换的现象。

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内容上下会有些衔接。。。

swich循环语句

	var n = 3;
	switch(n){
		case 1:
			console.log('a');
		case 2:
			console.log('b');
		case 3:
			console.log('c');
	}

这是一道题

	var n = 'a';
	switch(n) {
		case "a":
			console.log('a');break;
		case 2:
			console.log('b');break;
		case true:
			console.log('c');break;

	}

这是一道题

	var date = window.prompt('inout');
	switch(date) {
		case "monday":
		case "tuesday":
		case "wednesday":
		case "thursday":
		case "friday":
			console.log('working');break;
		case "saturday":
		case "sunday":
			console.log('relax');break;

	}

这是一道题

	var i = 0;
	while(1){
		i ++;
		console.log(i);
		if(i > 100){
			break;
		}
	}

这是一道题

	var i = 0;
	var sum = 0;
	for (i = 0; i < 100; i++) {
		sum += i;
		console.log(i);
		if (sum > 100) {
			break;
		}
	}

这是一道题

	for (var i = 0; i < 100; i++) {
		if (i % 7 == 0 || i % 10 == 7) {
			continue;
		}
		console.log(i);
	}
	// continue直接开始下一次循环

这是一道题

	var  arr = [1,2,3,4,6,'da',"gasf",undefined];
	for (var i = 0; i < arr.length; i++) {
				console.log(arr[i])；
	}

这是一道题

		var deng = {
		lastname : "Deng",
		age : 40,
		sex : undefined,
		wife : "xiaoliu",
		father : "dengdaye",
		son : "xiaodeng",
		handsome : false,
	}
	console.log(deng.lastname);
	deng.lastname = "Old Deng";
	console.log(deng.lastname);

1.面向过程
2.面向对象

typeof可以返回number string boolean object undefined function

	var num = function(){};
	console.log(typeof(num));

	var num = 123;
	console.log(typeof(num));

	var num = 1 * "1";
	console.log(typeof(num) + " : " + num);

类型转换

	var demo = "123";
	var num = Number(demo);
	console.log(typeof(num) + " : " + num);

	var demo = "123abc";
	var num = parseInt(demo);
	console.log(typeof(num) + " : " + num);

	var demo = "10";
	var num = parseInt(demo, 16);     //以16为基底转化成10进制
	console.log(typeof(num) + " : " + num);

	var demo = "123.33fefsd";
	var num = parseFloat(demo);
	console.log(typeof(num) + " : " + num);

	var demo = "123.3212adsdwa";
	var num = String(demo);
	console.log(typeof(num) + " : " + num);

	var demo = "123";
	var num = Boolean(demo);
	console.log(typeof(num) + " : " + num);

	var demo = "20";
	var num = demo.toString(8);  //把demo的值转化成8进制的数的结果
	console.log(typeof(num) + " : " + num);

	把二进制10000转化成16进制的数
	var num = 10000;
	var text =  parseInt(num,2);
	console.log(text.toString(16));

隐式类型转换

	console.log(isNaN(null));
	
	var a = "abc";
	a ++;
	console.log(a + " : " + typeof(a));

	var a = "a" + 1;
	console.log(a + " : " + typeof(a));

	var a = 1 == true;
	console.log(a + " : " + typeof(a));

	var a = 1 === "1";
	console.log(a + " : " + typeof(a));

	console.log(typeof(typeof(a)));

	console.log(typeof(a + ""));

这是一群题

	  alert(typeof(a));
	  
 	  alert(typeof(undefined));
 	  
 	  alert(typeof(NaN));
 	  
 	  alert(typeof(null));
 	  
 	  var a ="123abc";
 	  
 	  alert(typeof(+a));
 	  
 	  alert(typeof(!!a));
 	  
 	  alert((typeof(a +""));
 	  
 	  alert(1=="1");
 	  
 	  alert(NaN == NaN);
 	  
 	  alert(NaN == undefined);
 	  
 	  alert("11" + 11);
 	  
 	  alert(1==="1");
 	  
 	  alert(parselnt("123abc")) ;
 	  
 	  var num = 123123.345789;
 	  
 	  alert(num.toFixed(3));