Function mergeOptions

06.Router/basic/js/vue.js:1885–1918

* Merge two option objects into a new one. * Core utility used in both instantiation and inheritance. * * @param {Object} parent * @param {Object} child * @param {Vue} [vm] - if vm is present, indicates this is * an instantiation merge.

(parent, child, vm)

   */

  function mergeOptions(parent, child, vm) {
    guardComponents(child);
    guardProps(child);
    if ('development' !== 'production') {
      if (child.propsData && !vm) {
        warn('propsData can only be used as an instantiation option.');
      }
    }
    var options = {};
    var key;
    if (child['extends']) {
      parent = typeof child['extends'] === 'function' ? mergeOptions(parent, child['extends'].options, vm) : mergeOptions(parent, child['extends'], vm);
    }
    if (child.mixins) {
      for (var i = 0, l = child.mixins.length; i < l; i++) {
        var mixin = child.mixins[i];
        var mixinOptions = mixin.prototype instanceof Vue ? mixin.options : mixin;
        parent = mergeOptions(parent, mixinOptions, vm);
      }
    }
    for (key in parent) {
      mergeField(key);
    }
    for (key in child) {
      if (!hasOwn(parent, key)) {
        mergeField(key);
      }
    }
    function mergeField(key) {
      var strat = strats[key] || defaultStrat;
      options[key] = strat(parent[key], child[key], vm, key);
    }
    return options;
  }

  /**
   * Resolve an asset.