记录-js基础练习题

这里给大家分享我在网上总结出来的一些知识,希望对大家有所帮助

隔行换色(%):

window.onload = function() {
    var aLi = document.getElementsByTagName('li');
    for(var i = 0; i < aLi.length; i++){
        if(i%2 == 1){
			aLi[i].style.background = '#bfa';
        }
    }
}
<ul>
    <li>aaa</li>
	<li>bbb</li>
	<li>ccc</li>
	<li>ddd</li>
</ul>

简易计算器:

<script>
	window.onload = function(){
		var oNum1 = document.getElementById('num1');
        var oNum2 = document.getElementById('num2');
        var oBtn = document.getElementById('btn');
        var oSel = document.getElementById('sel');
        oBtn.onclick = function(){
            var iNum1 = parseInt(oNum1.value);
            var iNum2 = parseInt(oNum2.value);
            switch(oSel.value){
				case '+':
                	alert(iNum1+iNum2);
                break;
                case '-':
               		alert(iNum1-iNum2);
                break;
                case '*':
                	alert(iNum1*iNum2);
                break;
                case '/':
                	alert(iNum1/iNum2);
                break;
                default:
                	alert('你没有合适的运算符!');
                break;
            }
        }
	}
</script>
<input type="text" id = "num1">
<select name="" id="sel">
	<option value="+">+</option>
	<option value="-">-</option>
	<option value="*">*</option>
	<option value="/">/</option>
</select>
<input type="text" id="num2">
<input type="button" value="计算" id="btn">

双色球随机数生成:

目标:生成一组(7个) 1-33之间的随机不重复的整数(1.生成一个1-33之间的整数。 2.生成7个–>循环长度不固定用while循环。 3.要求不重复,补零操作)

<script>
    function rnd(m, n) {
    return m + parseInt(Math.random()*(n-m));
	}
	//数组去重
	function findInArr(num,arr) {
		for(var i = 0; i < arr.length; i++) {
            if(arr[i] == num){
                return true;
            }
        }
        return false;
    }
	function toDo(n){
        return n < 10 ? '0' + n : '' + n;
    }
	var arr = [];
	while(arr.length < 7) {
        //1-34包括1,不包括34
        var rNum = rnd(1,34);
        if(findInArr(rNum,arr) == false) {
            arr.push(toDo(rNum));
        }
    }
	document.write(arr);
</script>

鼠标滑过div显示隐藏:

<div id="box1"
   οnmοuseοver="document.getElementById('box1').style.width='200px';document.getElementById('box1').style.height='200px'"
     οnmοuseοut="document.getElementById('box1').style.width='100px';document.getElementById('box1').style.height='100px'">
</div>

条件判断if:

点击按钮,如果div显示,那么隐藏它,如果div隐藏,那么显示它。

<input type="button" value="显示隐藏" οnclick="showHide()">
<div id="box1"></div>
<script>
        function showHide() {
            var oDiv = document.getElementById('box1');
            if (oDiv.style.display == "block") {
                oDiv.style.display = "none";
            } else {
                oDiv.style.display = "block";
            }
        }
</script>

背景色换肤功能:

一个页面两个按钮,一个div点击不同的按钮,背景色分别变成不同的颜色,字体大小也要改变。

<style>
        #box1 {
            width: 200px;
            height: 200px;
            background-color: #bfa;
        }
        .day{
            background: green;
            font-size: 10px;
        }
        .night{
            background: gray;
            font-size: 22px;
        }
</style>
<input type="button" value="白天" οnclick="showDay()">
<input type="button" value="夜晚" οnclick="showNight()">
<div id="box1">实现白天夜晚换肤功能</div>
<script>
        function showDay(){
            document.body.className="day";   
        }
        function showNight(){
            document.body.className="night";
        }
</script>

行为和结构的分离:

<script>
	window.onload = function(){
		//1.获取元素
		var oBtn = document.getElementById('btn');
		//2.加事件
		oBtn.onclick = function(){
			alert();
		};
	};
</script>

全选功能的实现:

<script>
window.onload = function () {
	var oA = document.getElementById('all');
	var oBox = document.getElementById('box');
	//获取一组元素
	var oInp = oBox.getElementsByTagName('input');
	oA.onclick = function () {
		for (var i = 0; i < oInp.length; i++) {
			oInp[i].checked = true;
		}
	};
};
</script>
<input type="button" value="全选" id="all">
<hr>
<div id="box">
	<input type="checkbox" name="">
	<input type="checkbox" name="">
	<input type="checkbox" name="">
	<input type="checkbox" name="">
</div>

操作元素类容和属性的两种方式:

①方式:

window.onload = function(){
	var oBtn = document.getElementById('btn');
	oBtn.style.background = 'red';
	//方式二能实现1实现不了的功能oBtn['style']['background'] = 'green';
    //var aaa = 'background';
    //oBtn.style[aaa] = 'green';能够使用变量
}

②内容:

  1. 表单元素:oBtn.value
  2. 非表单元素:

    前端学习

    oP.innerHTML

反选功能实现:

window.onload = function() {
	var oR = document.getElementById('reverse');
	var oC = document.getElementById('C1');
	oR.onclick = function(){
		if(oC.checked == true){
            oC.checked = false;
		}else{
            oC.checked = true
        }
	}
} 
<input type = "button"  value="单个复选框反选" id="reverse">
<input type="checkbox" name="" id="C1">
    //这样写太麻烦了,不够简洁。改变如下:
<script>
	window.onload = function() {
		var oR = document.getElementById('reverse');
		var oC = document.getElementById('C1');
		oR.onclick = function() {
			oC.checked = !oC.checked;
		}
	}
</script>
<input type="button" value="单个复选框反选" id="reverse">
<input type="checkbox" name="" id="C1">

联动选择:

需求:点击上面的全选,那么下面都选中,如果下面全选中,那么上面也选中,如果下面有一个没选中,那么上面不选中。

<script>
    window.onload = function() {
		var oA = document.getElementById('all');
    	var oBox = document.getElementById('box');
    	var oInp = oBox.getElementsByTagName('input');
    	oA.onclick = function(){
            for(var i = 0; i < oInp.length; i++){
                oInp[i].checked = oA.checked;
            }
        };
    
    	for(var i = 0; i < oInp.length; i++){
			oInp[i].onclick = function() {
				var count = 0;
                for(var i = 0; i < oInp.length; i++){
                    if(oInp[i].checked){
                        count++;
                    }
                }
                if(count == oInp.length){
                    oA.checked = true;
                }else{
                    oA.checked = false;
                }
            }
        }
}
</script>
<input type="checkbox" name id="all">全选
<hr>
<div id="box">
    <input type="checkbox">
    <input type="checkbox">
    <input type="checkbox">
</div>
//为什么必须加一个box

选项卡实现(排他思想):

for循环是一瞬间完成的

<style>
	#box .on{
		background:#bfa;
	}
	#box div{
		width:300px;
		height:200px;
		border:1px solid red;
		display: none;
	}
</style>
<script>
	window.onload = function(){
		var oBox = document.getElementById('box');
		var oBtn = oBox.getElementsByTagName('input');
		var oDiv = oBox.getElementsByTagName('div');
		for(var i = 0; i < oBtn.length; i++){
            oBtn[i].index = i;
            oBtn[i].onclick = function(){
                for(var i = 0; i < oBtn.length; i++){
					oBtn[i].className = '';
                    oDiv[i].style.display = 'none';
                }
                this.className = 'on';
                oDiv[this.index].style.display = 'block';
            }
        }
	}
</script>
<div id = "box">
	<input type="button" value="体育" class="on">
	<input type="button" value="娱乐">
	<input type="button" value="新闻">
	<div style="display='block'">***获得100米第一</div>
	<div>段奕宏真帅!</div>
	<div>美国懂王昨日于白宫遭**</div>
</div>

简易定时器:

<script>
    window.onload = function() {
		var oTime = document.getElementById('time');
    	var oStart = document.getElementById('start');
    	var oStop = document.getElementById('stop');
    	var timer = null;
    	function toDo(n){
            return n < 10 ? '0' + n : n;
        }
    	oStart.onclick = function() {
            var s = 0;
            clearInterval(timer);
			timer = setInterval(function(){
                s++;
                oTime.value = toDo(parseInt(s / 60)) + ':' + toDo( s % 60);
            },50);	
        };
    	oStop.onclick = function() {
			clearInterval(timer);
        }
	};
</script>
<input type = "text" value="00:00" id = "time">
<input type = "button" value="开始" id="start">
<input type = "button" value = "停止" id = "stop">

文字时钟:

<script>
    window.onload = function() {
		var oP = document.getElementById('p1');
    	var timer = null;
    	function toDo(n) {
			return n < 10 ? '0' + n : n;
        }
    	function time() {
            var arr = ['日', '一', '二', '三', '四', '五','六'];
            var oDate = new Date();
            var year = oDate.getFullYear();
            var month = oDate.getMonth() + 1;
            var date = oDate.getDate();
            var w = oDate.getDay();
            var h = oDate.getHours();
            var m = oDate.getMinutes();
            var s = oDate.getSeconds();
            oP.innerHTML = year + '年' + month + '月' + date + '日' +toDo(h) +':' + toDo(m) + ':' + toDo(s) + '星期' + arr[w]; 
        }
    	time();//不需要等一秒钟再执行函数
    	clearInterval(timer);//定时器先关闭再执行
    	timer = setInterval(time,1000);    	
	}
</script>
<p id="p1">2020年8月20日15:56:30星期四</p>

延迟广告:

图片2s后显示,2s后消失,当鼠标移入图片时,不消失,移出后2s消失。

定时器里面可以套定时器

<script>
	window.onload = function() {
		var oImg = document.getElementById('pic');
        var timer = null;
        var timer2 = null;
        clearTimeout(timer);
        timer = setTimeout(function(){
        	oImg.style.display = 'block';
        	clearTimeout(timer2);
        	timer2 = setTimeout(function(){
        		oImg.style.display = 'none';
        	},2000);
        },2000);    
        oImg.onmouseover= function(){
        	clearTimeout(timer2);
        };
        oImg.onmouseout = function(){
        	timer2 = setTimeout(function(){
        		oImg.style.display = 'none';
        	},2000);
        };
	};
</script>
<img src="../image/1.jpg" id="pic">

自定义属性:

<script>
	window.onload = function(){
		var oBtn = document.getElementById('btn');
		oBtn.abc = 0; //自定义属性
		oBtn.onclick = function(){
			alert(this.abc);
		}
	};
</script>
<input type="button" value="aaa" id="btn">

轮播图(重点):

<style>
	#box .on{
		background: #bfa;
	}
	#box div{
		width: 300px;
		height: 200px;
		border: 1px solid red;
        display: none;
	}
</style>
<script>
	window.onload = function() {
		var oBox = document.getElementById('box');
		var oPrev = document.getElementById('prev');
		var oNext = document.getElementById('next');
		var oBtn = oBox.getElementsByTagName('input');
		var oDiv = oBox.getElementsByTagName('div');
		var iNow = 0;
		for(var i = 0; i < oBtn.length; i++){
			oBtn[i].index = i;
			oBtn[i].onclick = function(){
				iNow = this.index;
				for(var i = 0; i < oBtn.length; i++){
					oBtn[i].className='';
					oDiv[i].style.display='none';
				}
				this.className='on'; //this=oBtn[iNow]
				oDiv[this.index].style.display='block';
			};
		}
		//下一个播放
		oNext.onclick = function(){
			for(var i = 0; i < oBtn.length; i++){
				oBtn[i].className='';
				oDiv[i].style.display='none';
			}
			iNow++;
			if(iNow == oBtn.length){iNow = 0;}
			oBtn[iNow].className='on';
			oDiv[iNow].style.display='block';
		};
		//上一个播放
		oPrev.onclick = function(){
			for(var i = 0; i < oBtn.length; i++){
				oBtn[i].className='';
				oDiv[i].style.display='none';
			}
			iNow--;
			if(iNow == -1){iNow = oBtn.length - 1;}
			oBtn[iNow].className='on';
			oDiv[iNow].style.display='block';
		};		
	};
</script>
<div id="box">
	<a href="javascript:;" id="prev"><-</a>
    <input type="button" value="aaa" class="on">
    <input type="button" value="bbb">
    <input type="button" value="ccc">
    <a href="javascript:;" id="next">-></a>
    <div style="display:block">aaa</div>
    <div>bbb</div>
    <div>ccc</div>
</div>

简化代码(封装)+ 实现自动播放功能 如下:

<script>
	window.onload = function() {
		var oBox = document.getElementById('box');
		var oPrev = document.getElementById('prev');
		var oNext = document.getElementById('next');
		var oBtn = oBox.getElementsByTagName('input');
		var oDiv = oBox.getElementsByTagName('div');
		var iNow = 0;
    	var timer = null;
    	function tab(){
            for(var i = 0; i < oBtn.length; i++){
				oBtn[i].className='';
				oDiv[i].style.display='none';
			}			
			oBtn[iNow].className='on';
			oDiv[iNow].style.display='block';
        }
		for(var i = 0; i < oBtn.length; i++){
			oBtn[i].index = i;
			oBtn[i].onclick = function(){
				iNow = this.index;
				tab();
			};
		}
		//下一个播放
    	function fnNext(){
            iNow++;
			if(iNow == oBtn.length){iNow = 0;}
            tab();
        }
		oNext.onclick = fnNext;
		//上一个播放
		oPrev.onclick = function(){			
            iNow--;
			if(iNow == -1){iNow = oBtn.length - 1;}
            tab();
		};
    	//自动播放
    	clearInterval(timer);
    	timer = setInterval(function(){
            fnNext();
        },1000);
    	oBox.onmouseover = function(){
			clearInterval(timer);
        };
    	oBox.onmouseout = function(){
            clearInterval(timer);
          	timer = setInterval(function(){
                fnNext();
            },1000);  
        };
	};
</script>

理解立即执行函数:

var a = 12;
alert((a)); //2层括号不影响结果
var show = function(){};
show(); //(show)()
;(function(){})();  //防止别人的代码影响自己的

(function(){
	var a = b = 10;
})();
console.log(a); //undefined
console.log(b); //10

简易发布留言:

<script>
	window.onload = function(){
		var oTxt=document.getElementById('txt');
        var oBtn=document.getElementById('btn');
        var oUl=document.getElementById('ul1');
        oBtn.onclick = function(){
			var oLi = document.createElement('li');
            oLi.innerHTML=oTxt.value;
            //oUl.insertBefore(oLi,oUl.children[0]);
            //如果父级下面没有元素,那么向后插入,有,则向前插入。兼容IE
            if(oUl.children.length == 0){
            	oUl.appendChild(oLi);
            }else{
            	oUl.insertBefore(oLi,oUl.children[0]);
            }
            oTxt.value = '';
		};
	};
</script>
<input type="text" id="txt">
<input type="button" value="发布" id="btn">
<ul id="ul1"></ul>

上移下移功能实现:

<script>
	window.onload = function(){
		var oUl = document.getElementById('ul1');
		var aPrev = oUl.getElementsByClassName('prev');
		//上移
		for(var i = 0; i < aPrev.length; i++){
			aPrev[i].onclick = function(){
				var obj = this.parentNode;
				if(obj == oUl.children[0]){
					alert('到头了');
					return;
				}
				
				var oPrev = obj.previousElementSibling || obj.previousSibling;
				oUl.insertBefore(obj,oPrev);
			};
		}
		//下移
		var aNext = oUl.getElementsByClassName('next');
		for(var i = 0; i < aNext.length; i++){
			aNext[i].onclick = function(){
				var obj = this.parentNode;
				if(obj == oUl.children[oUl.children.length-1]){
					alert('到底了');
					return;
				}
				
				var oNext = obj.nextElementSibling || obj.nextSibling;
				var oNext2 = oNext.nextElementSibling || oNext.nextSibling;
				oUl.insertBefore(obj,oNext2);
			};
		}
	};
</script>
<ul id="ul1">
	<li><span>0.床前明月光</span>
		<a href="javascript:;" class="prev">上移</a>
		<a href="javascript:;" class="next">下移</a></li>
	<li><span>1.疑是地上霜</span>
		<a href="javascript:;" class="prev">上移</a>
		<a href="javascript:;" class="next">下移</a></li>
	<li><span>2.举头望明月</span>
		<a href="javascript:;" class="prev">上移</a>
		<a href="javascript:;" class="next">下移</a></li>
	<li><span>3.低头思故乡</span>
		<a href="javascript:;" class="prev">上移</a>
		<a href="javascript:;" class="next">下移</a></li>	
</ul>

右下角悬浮框功能实现:
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-SwhN8Ctu-1598018747062)(C:\Users\Hrj201305042\AppData\Roaming\Typora\typora-user-images\image-20200821143137668.png)]

//物体实际占的距离
window.onload = function(){
	var oDiv = document.getElementById('div1');
	alert(oDiv.offsetHeight);
};
//关于滚动的距离
body{height:3000px;}
#btn{position:fixed; left:10px; top:200px;}
window.onscroll = function(){
	var oBtn = document.getElementById('btn');
	oBtn.onclick = function(){
		var sT = document.documentElement.scrollTop || document.body.scrollTop;
		alert(sT);
	};
};
//可视区的高度
window.onload = function(){
	var oBtn = document.getElementById('btn');
	oBtn.onclick = function(){
		alert(document.documentElement.clientHeight);	
	};
};
<script>  //窗口缩小onresize
	window.onresize = window.onload=window.onscroll=
    function(){
		if(window.navigator.userAgent.indexOf('MSIE 6.0')!=-1){
			var oDiv = document.getElementById('div1');
			var sT = document.documentElement.scrollTop	|| document.body.scrollTop;
        	var cH = document.documentElement.clientHeight;
        	var oH = oDiv.offsetHeight;
        	oDiv.style.top = sT + cH + oH +'px';
        }	
	};
</script>
<div id="div1"></div>

json和数组的区别:

json中每个元素是以字符串作为下标,数组则是以数字作为下标。json使用for in循环,数组一般使用for循环。

var json = {"name":"leo", "age":18};  var arr=["leo",18];

json是种数据格式,和JavaScript没有直接联系,js原生提供了部分json操作方法,是js数据交互最通用的数据格式之一

json和字符串互转:

①字符串转json:name=leo&age=18 => {“name”: “leo”, “age” : 18}

<script>	
	function url2json(str){
		var arr = str.split('&');
		var json = {};
		for(var i = 0; i < arr.length; i++){
			//[user = leo age = 18 class = javas]
			//arr[i].split('=')[0]  user
			//arr[i].split('=')[1]  leo
			//json['user'] = leo
			json[arr[i].split('=')[0]] = arr[i].split('=')[1];
		}
		return json
	}
	var str = 'user=leo&age=18&class=javas';
	console.log(url2json(str));
</script>

②json转字符串{“name”: “leo” , “age” : 18} => name=leo&age=18

function json2url(json){
	var arr = [];
	for(var name in json){
		//name user
		//json[name] leo
		arr.push(name + '=' + json[name]);
		['name=leo', 'age=18']
	}
	return arr.join('&');
}
var json = {user:"leo", age:18, class:"javas"};
alert(json2url(json));

文字输入框提示实现:

#box{position:relative;}
#box span{color:#ccc;position:absolute;left:6px;top:2px;}
<script>
	window.onload = function(){
		var oS = document.getElementById('s1');
		var oTxt = document.getElementById('txt');
		oTxt.onfocus = function(){
			oS.style.display = 'none';
		};
        oTxt.onblur = function(){
			if(oTxt.value == ''){
				oS.style.display = 'block';
			}
		};
		oS.onclick = function(){
			//oS.style.display = 'none';
			oTxt.focus();
		};
	};
</script>
<div id="box">
	<span id="s1">请输入内容</span>
	<input type="text" id="txt">
</div>

事件对象:

<script>
	window.onload = function(){
		var oBtn = document.getElementById('btn');
		oBtn.onclick = function(ev){
			var oEvent = ev||event;
			console.log(oEvent);
		};
	};
</script>
<input type="button" value="点击" id="btn">

事件冒泡:

document.onclick = function(){alert('document');};
<div id="div1" onclick="alert('div1')">
	<input type="button" value="按钮" onclick="alert('input')">
</div> //点击按钮,从里往外传,input->div1->document.
       //(父级没有事件也往上传)如果input的上级div不添加事件 input-> document
       
//取消冒泡:1标准:oEvent.stopPropagation&&oEvent.stopPropagation();
		2.IE: oEvent.cancelBubble&&(oEvent.cancelBubble=true);

//绑定事件:FF chrome
 oBtn.addEventListener('click',aaa,false);
//IE6-8 没有捕获阶段,只有冒泡
oBtn.attachEvent('onclick', aaa;

获取鼠标点击位置:

document.onclick = function(){
    //chrome , IE
	alert('left:' + event.clientX+',top:'+event.clientY);
};

div跟随鼠标移动:

鼠标移动,div跟随鼠标移动

实现:1.获取鼠标位置 2.赋值给div的left和top样式

#div1{width:200px;height:200px;background:#bfa;position:absolute;}
<script>	
	window.onload = function(){
		var oDiv = document.getElementById('div1');
		document.onmousemove = function(ev){
			var oEvent = ev || event;
			console.log('ev.clientX:' + oEvent.clientX + 'ev.clientY:' + oEvent.clientY);
			oDiv.style.left = oEvent.clientX + 'px';
			oDiv.style.top = oEvent.cilentY + 'px';
		};
	};
</script>
<div id="div1"></div>

本文转载于:

https://blog.csdn.net/qq_48687155/article/details/108159063

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