Tutorial Clear Field on Focus

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<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.

Tutorial Check if Number is Even/Odd

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function isEven(value) {
	if (value%2 == 0)
		return true;
	else
		return false;
}

Tutorial Check if Function Exists Before Calling

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When using scripts that are shared between different areas of a site, there may be cases where a function is called that doesn't exist. It makes sense on one page (the dependency is there) but not another. The difference is too slight to warrant forking the file into different versions. Instead, you can just check if the function exists before calling it to avoid the error:

if (typeof yourFunctionName == 'function') { 
  yourFunctionName(); 
}

Tutorial Check if font-family is Honored

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function checkFont(strFamily) {
  var objDiv = document.createElement('div');

  objDiv.style.fontFamily = strFamily;
  objDiv.appendChild(document.createTextNode('FONT TEST'));

  if (window.getComputedStyle) {
      return window.getComputedStyle(objDiv, null).getPropertyValue('font-family') === strFamily;
  }

  return objDiv.currentStyle.fontFamily === strFamily;
}

Usage

var iconFontHonored = checkFont('icomoon');

Reference URL

Tutorial Call Function with Random Timer

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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

View Demo

Tutorial Break Out of iframe

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if (top.location!= self.location) {
   top.location = self.location.href;
}

That will generally work, but there is a small chance of failure in the case that window is overridden. Here's a couple of clever alternatives from Nathan Smith:

<script>

// Break out of an iframe, if someone shoves your site
// into one of those silly top-bar URL shortener things.
//
// Passing `this` and re-aliasing as `window` ensures
// that the window object hasn't been overwritten.
//
// Example:
//   var window = 'haha, punked!';
//
// Note: Probably unnecessary, but just for kicks.

(function(window) {
  if (window.location !== window.top.location) {
    window.top.location = window.location;
  }
})(this);

</script>
<script>

// A more cryptic one-liner, to awe & impress.
//
// No need to protect `window` since `this` is
// immutable, and at the topmost level means
// `window` anyways. Here, we compare locations
// on the left side of the "&&" and execute the
// code in parenthesis if that condition is
// true (top location isn't iframe location).
//
// Otherwise, nothing happens. It's basically an
// if statement without wrapping curly brackets.
//
// Weird, I know. But pretty cool, right? :)

this.top.location !== this.location && (this.top.location = this.location);

</script>

Reference URL