The days of 800x600 screens are all but over, but most of us still try to accommodate 1024px wide screens. Hence the popularity of "960" width sites. This bookmarklet will resize the current browser window to that width and height. You know, so us web designers with giant monitors can see what it's like to be slummin' with a 1024 screen. Also, to see "the fold", if such a concept even matters anymore.
javascript:resizeTo(1024,768)

<textarea rows="10" cols="50" onclick="this.focus();this.select()" readonly="readonly">
example text
</textarea>

<script type="text/javascript">
       alert('ALERT!')
</script>

function randRange(data) {
var newTime = data[Math.floor(data.length * Math.random())];
return newTime;
}
function toggleSomething() {
var timeArray = new Array(200, 300, 150, 250, 2000, 3000, 1000, 1500);
// do stuff, happens to use jQuery here (nothing else does)
$("#box").toggleClass("visible");
clearInterval(timer);
timer = setInterval(toggleSomething, randRange(timeArray));
}
var timer = setInterval(toggleSomething, 1000);
// 1000 = Initial timer when the page is first loaded

<input type="text" onfocus="if(this.value == 'value') { this.value = ''; }" value="value" />

Replace "value" with the default value. If the field is selected, the default value will go away. If the user has previously changed the field value, it'll be left alone.
Alternatively, use onfocus="this.value='';" to always clear the field.

This is like a replacement for PHP's SCRIPT_NAME with JavaScript.

location.href.split('/').pop();
For example with this URL:
http://css-tricks.com/examples/ScriptName/index.php

This code:
document.write( location.href.split('/').pop() );
Would write to the page: "index.php"

<script type="text/javascript">
if (/MSIE (\d+\.\d+);/.test(navigator.userAgent)) { //test for MSIE x.x;
 var ieversion=new Number(RegExp.$1) // capture x.x portion and store as a number
 if (ieversion>=8)
  document.write("You're using IE8 or above")
 else if (ieversion>=7)
  document.write("You're using IE7.x")
 else if (ieversion>=6)
  document.write("You're using IE6.x")
 else if (ieversion>=5)
  document.write("You're using IE5.x")
}
else
 document.write("n/a")
</script>

<script type="text/javascript">
<!--
dayNames = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
dayNumber = new Date().getDay();
document.writeln('<link rel="stylesheet" type="text/css" href="' + dayNames[dayNumber] + '.css">');
//-->
</script>

<noscript>
<link rel="stylesheet" type="text/css" href="default.css">
</noscript>

This is one of the fastest and easiest ways of emptying an array. Of course there are may other ways,
but those usually include creation of a new array. This way you reuse the same array.

var myArray = ["one", "two", "three"];

// console.log( myArray ) => ["one", "two", "three"]

myArray.length = 0;

// console.log( myArray ) => []