数据类型

<script language="javascript">

</script>

<script type="text/javascript">

  var x=1.79e+308;

  x=x+1;

  alert(x);

</script>

<script language="javascript">

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<script type="text/javascript">

  var string1="this is \"a\" eisc.cn";

  var string2='this is "a" eisc.cn!';

  document.write("string1="+string1);

  document.write("string2="+string2);

</script>

---------------------------------------------

<script type="text/javascript">

var x;

var y=null;

var z=undefined;

document.write("x:"+x+"<br/>y:"+y+"<br/>z:"+z+"<br>");

if(x==null)

{

document.write(111);

}

if(x==y)

{

document.write(222);

}

if(x==undefined)

{

document.write(333);

}

</script>

-----------------------------------------------------

<script type="text/javascript">

var x;

var y=null;

var z=undefined;

document.write("x:"+x+"<br/>y:"+y+"<br/>z:"+z+"<br>");

if(x==null)

{

document.write(111);

}

if(x==y)

{

document.write(222);

}

if(x==undefined)

{

document.write(333);

}

</script>

----------------------------------------------------

<script language="javascript">

var w=5;

var x=20;

var y="eisc";

var z=true;

alert(""+w+x+y+z);

//空未赋值的字符串为 ""+   字符串加数字为连接，数字加数字为计算，运算符加减乘除按顺序执行，括号优先执行 

</script>