13.2.2 eval方法.html

javascript即用即差核心对象手册

<script>
function myArray(n,initvalue)
   {
      for(var i=0;i<n;i++)
         this[i]=initvalue;
      this.length=n;
   }
   //输出标题为0到9的10各按钮
 function writeBtn()
 {
   var strhead="<input type='button' onclick='writeValue(this)' name='btn";
   var strend=" '>";
   var num=10
   //利用构造函数创建数组
   var arr=new myArray(num,strhead);
   document.write("<form>");
   document.write("<input type='text' name='val'>");
   //修改数组元素并输出
   for(var i=0;i<num;i++)
   {
      //每5个按钮一行
	  if (i%5==0)
          document.write("<br>");
      arr[i]+=i+"' value=' "+i+strend;
      document.write(arr[i]);
   }
 }
 //输出加减乘除等功能健
 function writeKey()
 {
    var arrkey=new Array(" . "," + "," - "," ( "," ) "," × "," ÷ "," C ");
	var str="<input type='button' onclick='writeValue(this)' name='btn' value='";
	for(var i=0;i<arrkey.length;i++)
	{
	   if (i%5==0&&i!=0)
          document.write("<br>");
	   document.write(str+arrkey[i]+"'>");
	}
	document.write("<input type=button value=' =  ' onclick='getVal()'>");
 }
 //定义函数，去掉字符串两端的空格
 function trim(str)
 {
    return str.replace(/(^\s*)|(\s*$)/g,"");
 }
 //将按钮相对应的值显示在文本框
 function writeValue(btn)
 {
	if (btn.value!=" C ")
    	document.getElementById("val").value+=trim(btn.value);
	else
	    document.getElementById("val").value="";
 }
 //按下等号后计算结果
 function getVal()
 {
    var str=document.getElementById("val").value;
	str=str.replace("×","*");
	str=str.replace("÷","/"); 
	document.getElementById("val").value=eval(str);
 }
 writeBtn();
 document.write("<br>");
 writeKey();
</script>