JavaScript實現(xiàn)一個簡易的計算器實例代碼

<div class="errorHint" id="errorHint"><img src="https://github.com/crystalYY/calculator/blob/master/img/error.png?raw=true"></div>
	<table cellpadding="0">
		<tr>
			<th colspan="5">計算器</th>
		</tr>
		<tr>
			<td colspan="5">
				<input type="text" value="0" name="showResult">
			</td>
		</tr>
		<tr>
			<td><button>7</button></td>
			<td><button>8</button></td>
			<td><button>9</button></td>
			<td><button class="setChange" id="backSpace">退格</button></td>
			<td><button class="setChange" id="clearNum">C</button></td>
		</tr>
		<tr>
			<td><button>4</button></td>
			<td><button>5</button></td>
			<td><button>6</button></td>
			<td><button>+</button></td>
			<td><button>-</button></td>
		</tr>
		<tr>
			<td><button>1</button></td>
			<td><button>2</button></td>
			<td><button>3</button></td>
			<td><button>*</button></td>
			<td><button>/</button></td>
		</tr>
		<tr>
			<td><button>0</button></td>
			<td><button>.</button></td>
			<td><button>%</button></td>
			<td colspan="2"><button class="setChange" id="gainResult">Enter</button></td>
		</tr>
	</table>
	<script type="text/javascript" src='index.js'>		
	</script>

*{margin: 0px; padding: 0px;}
		.errorHint{position: absolute; left: 130px; top:-282px;}
		.showError{border:1px solid red;}
		table{ border: 2px solid #996c33; width: 550px; padding: 10px; margin: 150px auto; background:url(https://github.com/crystalYY/calculator/blob/master/img/bg2.jpg?raw=trueg) left center no-repeat; border-radius: 10px;}
		table td{
			text-align: center;
			width: 100px;
			height: 40px;
			padding-left: 2px;
			padding-bottom: 2px;
		}
		table th{
			font-size: 18px;
			font-family:'楷體';
			color: 	#8B0000;
		}
		table td button{
			width: 98%;
			height: 98%;
			font-size: 16px;
			font-family: 'Microsoft yahei';
			background: none;
			color: 	#8B4726;
			outline:none;
			border:1px solid #000;
			border-radius: 5px;
			cursor: pointer;
		}
		table td input{
			width: 100%;
			margin: 10px 0;
			padding: 5px;
			border:1px solid #996c33;
			box-sizing: border-box;						
			text-align: right;
			font-size: 16px;
			font-family: 'Microsoft yahei';
		}

var oinput=document.getElementsByTagName('input')[0];
		//獲取外部樣式
		function getStyle(obj, name)
		{
			if(obj.currentStyle)
			{
				return obj.currentStyle[name];
			}
			else
			{
				return getComputedStyle(obj, false)[name];
			}
		}
		//漸變動畫
		function move(obj,attr,tar){
			clearInterval(obj.timer);
			obj.timer=setInterval(function(){
				var cur=parseInt(getStyle(obj,attr));
				var itarget=parseInt(tar);
				var speed=(itarget-cur)/6;
				speed=speed>0?Math.ceil(speed):Math.floor(speed);
				obj.style[attr]=parseInt(getStyle(obj,attr))+speed+'px';
				if(speed==0){
					clearInterval(obj.timer);
				}
			},30);
		}
		//事件綁定函數(shù)
		function addEvent(obj,ev,fun){
			if(obj.attachEvent){
				obj.attachEvent('on'+ev,fun);
			}else{
				obj.addEventListener(ev,fun,false);
			}
		}
		//阻止默認(rèn)行為
		function stopEvent(ev){
			var e=ev||window.event;
			if(e.preventDefault){
				e.preventDefault();
			}
			else{
				e.returnValue=false;//ie
			}
		}
		//計算最終結(jié)果
		function getResult(){
			function evalResult(){
				var result=eval(oinput.value);
				return result;			
			}
			//捕獲異常
			try{
				var x=evalResult();
				return x;
			}
			catch (e){
				oinput.className='showError';
				var errorHint=document.getElementById('errorHint');
				move(errorHint,'top',0);
				setTimeout(function(){
					oinput.className='';
					move(errorHint,'top',-282);
				},2000);
				return oinput.value;
			}
		}
		//文本框獲取焦點，錯誤提示消失
		//按下回車得到結(jié)果
		function enterResult(ev){
			var e=ev||window.event;
			if(e.keyCode==13){
				stopEvent(ev);//阻止enter鍵的默認(rèn)行為
				var result=getResult();
				oinput.value=result;
			}
		}
		//綁定點擊事件
		function init(){
			var otable=document.getElementsByTagName('table')[0];
			addEvent(otable,'keydown',function(ev){
				enterResult(ev);
			});
			addEvent(otable,'click',function(ev){
				stopEvent(ev);
				var e=ev||window.event;
				var itat=e.target||e.srcElement;
				var obtns=document.getElementsByTagName('button');
				if(itat.nodeName.toLowerCase()=='button'){
					for(var i=0;i<obtns.length;i++){
						obtns[i].style.borderColor='#000';
					}
					itat.style.borderColor='white';
					if(itat.className!='setChange'){
						if(oinput.value=='0'){
							oinput.value='';
							oinput.value+=itat.innerHTML;
						}
						else{
							oinput.value+=itat.innerHTML;
						}
					}else{
						if(itat.id=='backSpace'){
							oinput.value=oinput.value.toString().slice(0,-1);
						}
						else if(itat.id=='clearNum'){
							oinput.value='0';
						}else{
							var result=getResult();
							oinput.value=result;
						}
					}
				}
			});
		}
		init();

function getResult(){
   function evalResult(){
    var result=eval(oinput.value);
    return result;   
   }
   //捕獲異常
   try{
    var x=evalResult();
    return x;
   }
   catch (e){
    oinput.className='showError';
    var errorHint=document.getElementById('errorHint');
    move(errorHint,'top',0);
    setTimeout(function(){
     oinput.className='';
     move(errorHint,'top',-282);
    },2000);
    return oinput.value;
   }
  }