数据类型转换函数
toString--转换成字符串；--所有数据类型均可转换成String类型
parseInt--强制转换成整数；如果不能转换则返回NaN
parseFloat--强制转换成浮点数，如果不能转换返回NaN
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3c.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<html xmlns="http://www.w3x.org/1999/xhtml"> <head> <title>Javascript Day01</title> <meta http-equlv="content-type" content="text/html;charset=utf-8"/> <script language="javascript" src="js_demo1.js" type="text/javascript"></script> <script language="javascript" type="text/javascript"> function firstMethod(){ alert("Hello World in script block."); } </script> </head> <form> <h2>1.Hello Word</h2> <input type="button" value="first button" οnclick="alert('Hello Word');"/> <input type="button" value="second button" οnclick="firstMethod();"/> <input type="button" value="third button" οnclick="secondMethod();"/> <h2>2.判断数据类型，并计算平方</h2> <input type="text" id="txtData"/><br/> <input type="button" value="计算平方" οnclick="getSquare()";/> </form> </body></html> js代码：function secondMethod(){
alert("hello world");}function getSquare(){ var str = document.getElementById("txtData").value; if(isNaN(str)) alert("请录入数值"); else{ var data=parseFloat(str); var result = data* data; alert(result); }}