January 5, 2012

Coffeescript: HTML5 <input> placeholder attribute fallback

You want to use the new HTML5 placeholder attribute on input fields, but you also want to support older browsers. Here's a little Coffeescript class that takes an HTML element in the constructor, and uses jQuery to bind the focus and blur events to swap out text like a modern browser would without the script.
# ## HTML5 placeholder feature fallback class
class PlaceholderFallback

  constructor: (el) ->
    @el = $(el)
  # HTML5 <input> placeholder feature detection
  browserHasPlaceholder: =>
    "placeholder" of document.createElement("input")
  # Reads the placeholder attribute and uses it in a javascript fallback, if needed
  initialize: =>
    if @browserHasPlaceholder() == false
      placeholderText = @el.attr 'placeholder' 
      @el.removeAttr 'placeholder'
      @el.focus (e) ->
        if this.value == placeholderText
          this.value = ''
      @el.blur (e) ->
        if this.value == ''
          this.value = placeholderText
      @el = null

# Usage:
placeholderFallback = new PlaceholderFallback( element )