Vue源码解析(一)

使用vue已经大半年时间了,写起来已经很顺手了。比起之前的jquery时代,vue配合webpack的使用,让前端代码整体性更强,代码量也比之前少了一些。用了一段时间后,也想了解Vue具体是如何实现这样的一个mvvm框架的,经过一段时间的挣扎,终于开始了源码解析。ps:本次解读的vue源码版本为2.3.3,本人水平有限,如果解析有误的地方,请批评指正。

首先,不管采用什么方式引入vue,直接script引入,requireJs引入等等等,vue都会进行相关的初始化工作。

function Vue$3 (options) {
  if ("development" !== 'production' 
    !(this instanceof Vue$3)
  ) {
    warn('Vue is a constructor and should be called with the `new` keyword');
  }
  this._init(options);
}

initMixin(Vue$3);
stateMixin(Vue$3);
eventsMixin(Vue$3);
lifecycleMixin(Vue$3);
renderMixin(Vue$3);
//全局Api的代码在比较靠下的位置
initGlobalAPI(Vue$3);

定义了Vue$3这个类,接着调用了initMixin、stateMixin、eventsMixin、lifecycleMixin、renderMixin、initGlobalAPI几个方法。

var uid$1 = 0;

function initMixin (Vue) {
  Vue.prototype._init = function (options) {
    var vm = this;
    // a uid
    vm._uid = uid$1++;

    var startTag, endTag;
    /* istanbul ignore if */
    if ("development" !== 'production'  config.performance  mark) {
      startTag = "vue-perf-init:" + (vm._uid);
      endTag = "vue-perf-end:" + (vm._uid);
      mark(startTag);
    }

    // a flag to avoid this being observed
    vm._isVue = true;
    // merge options
    if (options  options._isComponent) {
      // optimize internal component instantiation
      // since dynamic options merging is pretty slow, and none of the
      // internal component options needs special treatment.
      initInternalComponent(vm, options);
    } else {
      vm.$options = mergeOptions(
        resolveConstructorOptions(vm.constructor),
        options || {},
        vm
      );
    }
    /* istanbul ignore else */
    {
      initProxy(vm);
    }
    // expose real self
    vm._self = vm;
    initLifecycle(vm);
    initEvents(vm);
    initRender(vm);
    callHook(vm, 'beforeCreate');
    initInjections(vm); // resolve injections before data/props
    initState(vm);
    initProvide(vm); // resolve provide after data/props
    callHook(vm, 'created');

    /* istanbul ignore if */
    if ("development" !== 'production'  config.performance  mark) {
      vm._name = formatComponentName(vm, false);
      mark(endTag);
      measure(((vm._name) + " init"), startTag, endTag);
    }

    if (vm.$options.el) {
      vm.$mount(vm.$options.el);
    }
  };
}

initMixin方法,定义了Vue$3的_init的方法。startTag, endTag,mark为开启performance模式同时浏览器支持Performance.mark()方法时,在浏览器开发工具中对组件进行性能追踪。根据_isComponent是否为true调用initInternalComponent或mergeOptions进行options合并。

function initLifecycle (vm) {
  var options = vm.$options;

  // locate first non-abstract parent
  var parent = options.parent;
  if (parent  !options.abstract) {
    while (parent.$options.abstract  parent.$parent) {
      parent = parent.$parent;
    }
    parent.$children.push(vm);
  }

  vm.$parent = parent;
  vm.$root = parent ? parent.$root : vm;

  vm.$children = [];
  vm.$refs = {};

  vm._watcher = null;
  vm._inactive = null;
  vm._directInactive = false;
  vm._isMounted = false;
  vm._isDestroyed = false;
  vm._isBeingDestroyed = false;
}

生命周期初始化,找到第一个非抽象parent,在$children数组中添加vm。$children$refs 等设置初始值。

function initEvents (vm) {
  vm._events = Object.create(null);
  vm._hasHookEvent = false;
  // init parent attached events
  var listeners = vm.$options._parentListeners;
  if (listeners) {
    updateComponentListeners(vm, listeners);
  }
}

事件初始化,如果有父组件监听调用updateComponentListeners更新监听。

function initRender (vm) {
  vm._vnode = null; // the root of the child tree
  vm._staticTrees = null;
  var parentVnode = vm.$vnode = vm.$options._parentVnode; // the placeholder node in parent tree
  var renderContext = parentVnode  parentVnode.context;
  vm.$slots = resolveSlots(vm.$options._renderChildren, renderContext);
  vm.$scopedSlots = emptyObject;
  // bind the createElement fn to this instance
  // so that we get proper render context inside it.
  // args order: tag, data, children, normalizationType, alwaysNormalize
  // internal version is used by render functions compiled from templates
  vm._c = function (a, b, c, d) { return createElement(vm, a, b, c, d, false); };
  // normalization is always applied for the public version, used in
  // user-written render functions.
  vm.$createElement = function (a, b, c, d) { return createElement(vm, a, b, c, d, true); };
}

渲染初始化,调用resolveSlots方法返回vm子组件slots。渲染初始化结束后callHook(vm, ‘beforeCreate’)方法下发beforeCreate事件。

function initInjections (vm) {
  var result = resolveInject(vm.$options.inject, vm);
  if (result) {
    Object.keys(result).forEach(function (key) {
      /* istanbul ignore else */
      {
        defineReactive$$1(vm, key, result[key], function () {
          warn(
            "Avoid mutating an injected value directly since the changes will be " +
            "overwritten whenever the provided component re-renders. " +
            "injection being mutated: \"" + key + "\"",
            vm
          );
        });
      }
    });
  }
}

注入初始化。

function initState (vm) {
  vm._watchers = [];
  var opts = vm.$options;
  if (opts.props) { initProps(vm, opts.props); }
  if (opts.methods) { initMethods(vm, opts.methods); }
  if (opts.data) {
    initData(vm);
  } else {
    observe(vm._data = {}, true /* asRootData */);
  }
  if (opts.computed) { initComputed(vm, opts.computed); }
  if (opts.watch) { initWatch(vm, opts.watch); }
}

初始化props、methods、data、computed、watch。

function initProvide (vm) {
  var provide = vm.$options.provide;
  if (provide) {
    vm._provided = typeof provide === 'function'
      ? provide.call(vm)
      : provide;
  }
}

初始化provide。provide初始化结束后,调用callHook(vm, ‘created’)方法下发created事件。

if (vm.$options.el) {
      vm.$mount(vm.$options.el);
}

最后,如果option中el存在,挂载元素到对应的el上,之后进行组件的渲染。

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