js/libs/ember-1.5.1.js
function set(obj, keyName, value, tolerant) {
  if (typeof obj === 'string') {
    Ember.assert("Path '" + obj + "' must be global if no obj is given.", IS_GLOBAL.test(obj));
    value = keyName;
    keyName = obj;
    obj = null;
  }

  Ember.assert("Cannot call set with "+ keyName +" key.", !!keyName);

  if (!obj || keyName.indexOf('.') !== -1) {
    return setPath(obj, keyName, value, tolerant);
  }

  Ember.assert("You need to provide an object and key to `set`.", !!obj && keyName !== undefined);
  Ember.assert('calling set on destroyed object', !obj.isDestroyed);

  var meta = obj[META_KEY], desc = meta && meta.descs[keyName],
      isUnknown, currentValue;
  if (desc) {
    desc.set(obj, keyName, value);
  } else {
    isUnknown = 'object' === typeof obj && !(keyName in obj);

    // setUnknownProperty is called if `obj` is an object,
    // the property does not already exist, and the
    // `setUnknownProperty` method exists on the object
    if (isUnknown && 'function' === typeof obj.setUnknownProperty) {
      obj.setUnknownProperty(keyName, value);
    } else if (meta && meta.watching[keyName] > 0) {
      if (MANDATORY_SETTER) {
        currentValue = meta.values[keyName];
      } else {
        currentValue = obj[keyName];
      }
      // only trigger a change if the value has changed
      if (value !== currentValue) {
        Ember.propertyWillChange(obj, keyName);
        if (MANDATORY_SETTER) {
          if ((currentValue === undefined && !(keyName in obj)) || !obj.propertyIsEnumerable(keyName)) {
            Ember.defineProperty(obj, keyName, null, value); // setup mandatory setter
          } else {
            meta.values[keyName] = value;
          }
        } else {
          obj[keyName] = value;
        }
        Ember.propertyDidChange(obj, keyName);
      }
    } else {
      obj[keyName] = value;
    }
  }
  return value;
}
function set(obj, keyName, value, tolerant) {
  if (typeof obj === 'string') {
    Ember.assert("Path '" + obj + "' must be global if no obj is given.", IS_GLOBAL.test(obj));
    value = keyName;
    keyName = obj;
    obj = null;
  }

  Ember.assert("Cannot call set with "+ keyName +" key.", !!keyName);

  if (!obj || keyName.indexOf('.') !== -1) {
    return setPath(obj, keyName, value, tolerant);
  }

  Ember.assert("You need to provide an object and key to `set`.", !!obj && keyName !== undefined);
  Ember.assert('calling set on destroyed object', !obj.isDestroyed);

  var meta = obj[META_KEY], desc = meta && meta.descs[keyName],
      isUnknown, currentValue;
  if (desc) {
    desc.set(obj, keyName, value);
  } else {
    isUnknown = 'object' === typeof obj && !(keyName in obj);

    // setUnknownProperty is called if `obj` is an object,
    // the property does not already exist, and the
    // `setUnknownProperty` method exists on the object
    if (isUnknown && 'function' === typeof obj.setUnknownProperty) {
      obj.setUnknownProperty(keyName, value);
    } else if (meta && meta.watching[keyName] > 0) {
      if (MANDATORY_SETTER) {
        currentValue = meta.values[keyName];
      } else {
        currentValue = obj[keyName];
      }
      // only trigger a change if the value has changed
      if (value !== currentValue) {
        Ember.propertyWillChange(obj, keyName);
        if (MANDATORY_SETTER) {
          if ((currentValue === undefined && !(keyName in obj)) || !obj.propertyIsEnumerable(keyName)) {
            Ember.defineProperty(obj, keyName, null, value); // setup mandatory setter
          } else {
            meta.values[keyName] = value;
          }
        } else {
          obj[keyName] = value;
        }
        Ember.propertyDidChange(obj, keyName);
      }
    } else {
      obj[keyName] = value;
    }
  }
  return value;
}
Sets the value of a property on an object, respecting computed properties
and notifying observers and other listeners of the change. If the
property is not defined but the object implements the `setUnknownProperty`
method then that will be invoked as well.

@method set
@for Ember
@param {Object} obj The object to modify.
@param {String} keyName The property key to set
@param {Object} value The value to set
@return {Object} the passed value.