jsmodules/Mixins.js

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 * The Original Code is Snowl.
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 *
 * Contributor(s):
 *   Myk Melez <myk@mozilla.org>
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let EXPORTED_SYMBOLS = ["Mixins"];

/**
 * Mix attributes (properties, methods, getters/setters) from the source object
 * into the target object.
 *
 * Note: doesn't mix in attributes that already exist in the target object
 * (i.e. doesn't override existing attributes).
 * ??? Should it?
 * 
 * FIXME: give the target object access in some way to the source's version
 * of attributes it overrides.
 *
 * @param   source  {Object}  the object that provides attributes
 * @param   target  {Object}  the object that receives attributes
 */
function mixin(source, target) {
  for (let attribute in source) {
    // Don't mix in attributes that already exist in the target.
    if (attribute in target)
      continue;

    let getter = source.__lookupGetter__(attribute);
    let setter = source.__lookupSetter__(attribute);

    // We can have a getter, a setter, or both.  If we have either, we only
    // define one or both of them.  Otherwise, we assign the property directly.
    if (getter || setter) {
      if (getter)
        target.__defineGetter__(attribute, getter);
      if (setter)
        target.__defineSetter__(attribute, setter);
    }
    else
       target[attribute] = source[attribute];
  }
}

// FIXME: support both source and target arguments accepting arrays of objects.
let Mixins = {
  mix: function(source) {
    return {
      source: source,
      into: function(target) {
        mixin(this.source, target);
      }
    };
  }
};