Simple JavaScript feature detection.

featuretest.js

var testFeature = (function () {

  return {

    /**
     * Accepts a feature name and feature test function to test for truthness
     * @param {String} featureName of the feature being tested
     * @param {Function} testMethod the feature test method ( this should always return true or false )
     */
    addTest: function( featureName, testMethod ) {
      if ( typeof featureName === 'string' && typeof testMethod === 'function' ) {
        this.addClass( featureName, testMethod() );
      }
    },

    /**
     * Adds a class to the html element for each feature name
     * the class is "featureName" if it's supported otherwise it's "no-featureName"
     * @param {String} featureName name of the feature being tested
     * @param {Bool} featureSupported is the feature supported?
     */
    addClass: function( featureName, featureSupported ) {
      document.documentElement.className += ' ' + ( featureSupported ) ? featureName : 'no-' + featureName;
    }
  };

}());


testFeature.addTest('fileinput', function () {
  // feature tests logic goes in here and must return true or false.
});