先看index.html的代码吧

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>mini Vue</title>
</head>

<body>
  <div id='app'>
  </div>
</body>
<script src='./utils.js'></script>
<script src='./index.js'></script>

<script>
  var vm = new Vue({
    name: 'root',
    el: '#app',
    render(h) {
      return h('div', 'ok');
    },
  });
  console.log('vm ', vm);
</script>
</html>

基本就是vue的index.html加上main.js的结合体,这里为了避免index.js太长,把一些基础方法放到了utils.js里面
具体代码见github地址:https://github.com/shadowprompt/miniVue

本系列查看的源码是vue 2.6.10,文件是node_modules/vue/dist/vue.runtime.esm.js

首先是通过一系列的mixin操作,在Vue.protoype上面加入一系列方法

先看initMixin。因为在Vue的构造函数里面需要执行this._init(options)

Vue.prototype._init = function (options) {
    var vm = this;
    // a uid
    vm._uid = uid$3++;

    var startTag, endTag;
    /* istanbul ignore if */
    if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
      startTag = "vue-perf-start:" + (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 */
    if (process.env.NODE_ENV !== 'production') {
      initProxy(vm);
    } else {
      vm._renderProxy = 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 (process.env.NODE_ENV !== 'production' && config.performance && mark) {
      vm._name = formatComponentName(vm, false);
      mark(endTag);
      measure(("vue " + (vm._name) + " init"), startTag, endTag);
    }

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

看上去比较大“简单”,但是里面每一个initXXX都是大家伙。
这里先提下initRender(vm)

function initRender (vm) {
  vm._vnode = null; // the root of the child tree
  vm._staticTrees = null; // v-once cached trees
  var options = vm.$options;
  var parentVnode = vm.$vnode = options._parentVnode; // the placeholder node in parent tree
  var renderContext = parentVnode && parentVnode.context;
  vm.$slots = resolveSlots(options._renderChildren, renderContext);
  vm.$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); };

  // $attrs & $listeners are exposed for easier HOC creation.
  // they need to be reactive so that HOCs using them are always updated
  var parentData = parentVnode && parentVnode.data;

  /* istanbul ignore else */
  if (process.env.NODE_ENV !== 'production') {
    defineReactive$$1(vm, '$attrs', parentData && parentData.attrs || emptyObject, function () {
      !isUpdatingChildComponent && warn("$attrs is readonly.", vm);
    }, true);
    defineReactive$$1(vm, '$listeners', options._parentListeners || emptyObject, function () {
      !isUpdatingChildComponent && warn("$listeners is readonly.", vm);
    }, true);
  } else {
    defineReactive$$1(vm, '$attrs', parentData && parentData.attrs || emptyObject, null, true);
    defineReactive$$1(vm, '$listeners', options._parentListeners || emptyObject, null, true);
  }
}

其中vm.$createElement = function (a, b, c, d) { return createElement(vm, a, b, c, d, true); };,可以看出我们的vm.$createElement并不是通过原型写进去的方法,而是每次_init时写进去的,createElement就是我们会使用render的写法(render: h => h('div', '这是个div'))时的参数,用来创建vnode的。

var SIMPLE_NORMALIZE = 1;
var ALWAYS_NORMALIZE = 2;

// wrapper function for providing a more flexible interface
// without getting yelled at by flow
function createElement (
  context,
  tag,
  data,
  children,
  normalizationType,
  alwaysNormalize
) {
  if (Array.isArray(data) || isPrimitive(data)) {
    normalizationType = children;
    children = data;
    data = undefined;
  }
  if (isTrue(alwaysNormalize)) {
    normalizationType = ALWAYS_NORMALIZE;
  }
  return _createElement(context, tag, data, children, normalizationType)
}

function _createElement (
  context,
  tag,
  data,
  children,
  normalizationType
) {
  if (isDef(data) && isDef((data).__ob__)) {
    process.env.NODE_ENV !== 'production' && warn(
      "Avoid using observed data object as vnode data: " + (JSON.stringify(data)) + "\n" +
      'Always create fresh vnode data objects in each render!',
      context
    );
    return createEmptyVNode()
  }
  // object syntax in v-bind
  if (isDef(data) && isDef(data.is)) {
    tag = data.is;
  }
  if (!tag) {
    // in case of component :is set to falsy value
    return createEmptyVNode()
  }
  // warn against non-primitive key
  if (process.env.NODE_ENV !== 'production' &&
    isDef(data) && isDef(data.key) && !isPrimitive(data.key)
  ) {
    {
      warn(
        'Avoid using non-primitive value as key, ' +
        'use string/number value instead.',
        context
      );
    }
  }
  // support single function children as default scoped slot
  if (Array.isArray(children) &&
    typeof children[0] === 'function'
  ) {
    data = data || {};
    data.scopedSlots = { default: children[0] };
    children.length = 0;
  }
  if (normalizationType === ALWAYS_NORMALIZE) {
    children = normalizeChildren(children);
  } else if (normalizationType === SIMPLE_NORMALIZE) {
    children = simpleNormalizeChildren(children);
  }
  var vnode, ns;
  if (typeof tag === 'string') {
    var Ctor;
    ns = (context.$vnode && context.$vnode.ns) || config.getTagNamespace(tag);
    if (config.isReservedTag(tag)) {
      // platform built-in elements
      vnode = new VNode(
        config.parsePlatformTagName(tag), data, children,
        undefined, undefined, context
      );
    } else if ((!data || !data.pre) && isDef(Ctor = resolveAsset(context.$options, 'components', tag))) {
      // component
      vnode = createComponent(Ctor, data, context, children, tag);
    } else {
      // unknown or unlisted namespaced elements
      // check at runtime because it may get assigned a namespace when its
      // parent normalizes children
      vnode = new VNode(
        tag, data, children,
        undefined, undefined, context
      );
    }
  } else {
    // direct component options / constructor
    vnode = createComponent(tag, data, context, children);
  }
  if (Array.isArray(vnode)) {
    return vnode
  } else if (isDef(vnode)) {
    if (isDef(ns)) { applyNS(vnode, ns); }
    if (isDef(data)) { registerDeepBindings(data); }
    return vnode
  } else {
    return createEmptyVNode()
  }
}

最后我们会调用$mount方法,我们直接看看它是怎么把node挂载到页面的

接着看这个mountComponent

<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<script>
     (adsbygoogle = window.adsbygoogle || []).push({
          google_ad_client: "ca-pub-3013839362871866",
          enable_page_level_ads: true
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</script>
function mountComponent (
  vm,
  el,
  hydrating
) {
  vm.$el = el;
  if (!vm.$options.render) {
    vm.$options.render = createEmptyVNode;
    if (process.env.NODE_ENV !== 'production') {
      /* istanbul ignore if */
      if ((vm.$options.template && vm.$options.template.charAt(0) !== '#') ||
        vm.$options.el || el) {
        warn(
          'You are using the runtime-only build of Vue where the template ' +
          'compiler is not available. Either pre-compile the templates into ' +
          'render functions, or use the compiler-included build.',
          vm
        );
      } else {
        warn(
          'Failed to mount component: template or render function not defined.',
          vm
        );
      }
    }
  }
  callHook(vm, 'beforeMount');

  var updateComponent;
  /* istanbul ignore if */
  if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
    updateComponent = function () {
      var name = vm._name;
      var id = vm._uid;
      var startTag = "vue-perf-start:" + id;
      var endTag = "vue-perf-end:" + id;

      mark(startTag);
      var vnode = vm._render();
      mark(endTag);
      measure(("vue " + name + " render"), startTag, endTag);

      mark(startTag);
      vm._update(vnode, hydrating);
      mark(endTag);
      measure(("vue " + name + " patch"), startTag, endTag);
    };
  } else {
    updateComponent = function () {
      vm._update(vm._render(), hydrating);
    };
  }

  // we set this to vm._watcher inside the watcher's constructor
  // since the watcher's initial patch may call $forceUpdate (e.g. inside child
  // component's mounted hook), which relies on vm._watcher being already defined
  new Watcher(vm, updateComponent, noop, {
    before: function before () {
      if (vm._isMounted && !vm._isDestroyed) {
        callHook(vm, 'beforeUpdate');
      }
    }
  }, true /* isRenderWatcher */);
  hydrating = false;

  // manually mounted instance, call mounted on self
  // mounted is called for render-created child components in its inserted hook
  if (vm.$vnode == null) {
    vm._isMounted = true;
    callHook(vm, 'mounted');
  }
  return vm
}

里面new了一个Watcher

new Watcher(vm, updateComponent, noop, {
    before: function before () {
      if (vm._isMounted && !vm._isDestroyed) {
        callHook(vm, 'beforeUpdate');
      }
    }
}, true /* isRenderWatcher */);

第二个参数就是watcher的getter
在创建Watcher时,在构造函数里面

if (typeof expOrFn === 'function') {
    this.getter = expOrFn;
  } else {
    this.getter = parsePath(expOrFn);
    if (!this.getter) {
      this.getter = noop;
      process.env.NODE_ENV !== 'production' && warn(
        "Failed watching path: \"" + expOrFn + "\" " +
        'Watcher only accepts simple dot-delimited paths. ' +
        'For full control, use a function instead.',
        vm
      );
    }
  }
  this.value = this.lazy
    ? undefined
    : this.get();

除了是lazy的情况,我们在创建实例的时候是会直接调用this.get()

Watcher.prototype.get = function get () {
  pushTarget(this); // targetStack.push(target); Dep.target = target;
  var value;
  var vm = this.vm;
  try {
    value = this.getter.call(vm, vm);
  } catch (e) {
    if (this.user) {
      handleError(e, vm, ("getter for watcher \"" + (this.expression) + "\""));
    } else {
      throw e
    }
  } finally {
    // "touch" every property so they are all tracked as
    // dependencies for deep watching
    if (this.deep) {
      traverse(value);
    }
    popTarget();
    this.cleanupDeps();
  }
  return value
};

在这里我们调用get的话,实际调用的是updateComponent,也就是vm._update(vm._render(), hydrating);
我们先按参数 vm._render(),它会返回一个vnode,代码如下:

Vue.prototype._render = function () {
    var vm = this;
    var ref = vm.$options;
    var render = ref.render;
    var _parentVnode = ref._parentVnode;

    if (_parentVnode) {
      vm.$scopedSlots = normalizeScopedSlots(
        _parentVnode.data.scopedSlots,
        vm.$slots,
        vm.$scopedSlots
      );
    }

    // set parent vnode. this allows render functions to have access
    // to the data on the placeholder node.
    vm.$vnode = _parentVnode;
    // render self
    var vnode;
    try {
      // There's no need to maintain a stack becaues all render fns are called
      // separately from one another. Nested component's render fns are called
      // when parent component is patched.
      currentRenderingInstance = vm;
      vnode = render.call(vm._renderProxy, vm.$createElement);
    } catch (e) {
      handleError(e, vm, "render");
      // return error render result,
      // or previous vnode to prevent render error causing blank component
      /* istanbul ignore else */
      if (process.env.NODE_ENV !== 'production' && vm.$options.renderError) {
        try {
          vnode = vm.$options.renderError.call(vm._renderProxy, vm.$createElement, e);
        } catch (e) {
          handleError(e, vm, "renderError");
          vnode = vm._vnode;
        }
      } else {
        vnode = vm._vnode;
      }
    } finally {
      currentRenderingInstance = null;
    }
    // if the returned array contains only a single node, allow it
    if (Array.isArray(vnode) && vnode.length === 1) {
      vnode = vnode[0];
    }
    // return empty vnode in case the render function errored out
    if (!(vnode instanceof VNode)) {
      if (process.env.NODE_ENV !== 'production' && Array.isArray(vnode)) {
        warn(
          'Multiple root nodes returned from render function. Render function ' +
          'should return a single root node.',
          vm
        );
      }
      vnode = createEmptyVNode();
    }
    // set parent
    vnode.parent = _parentVnode;
    return vnode
};

在处理完normalizeScopedSlots后调用了render方法:vnode = render.call(vm._renderProxy, vm.$createElement)
接着看_update方法

Vue.prototype._update = function (vnode, hydrating) {
    var vm = this;
    var prevEl = vm.$el;
    var prevVnode = vm._vnode;
    var restoreActiveInstance = setActiveInstance(vm);
    vm._vnode = vnode;
    // Vue.prototype.__patch__ is injected in entry points
    // based on the rendering backend used.
    if (!prevVnode) {
      // initial render
      vm.$el = vm.__patch__(vm.$el, vnode, hydrating, false /* removeOnly */);
    } else {
      // updates
      vm.$el = vm.__patch__(prevVnode, vnode);
    }
    restoreActiveInstance();
    // update __vue__ reference
    if (prevEl) {
      prevEl.__vue__ = null;
    }
    if (vm.$el) {
      vm.$el.__vue__ = vm;
    }
    // if parent is an HOC, update its $el as well
    if (vm.$vnode && vm.$parent && vm.$vnode === vm.$parent._vnode) {
      vm.$parent.$el = vm.$el;
    }
    // updated hook is called by the scheduler to ensure that children are
    // updated in a parent's updated hook.
};

其实__patch__方法就是var patch = createPatchFunction({ nodeOps: nodeOps, modules: modules });
createPatchFunction是个很重要的方法,是将vnode变成真实dom,然后挂载到对应的父节点下面。
里面会递归的调用createElmcreateChildren

function createPatchFunction(){
    ....
    return function patch (oldVnode, vnode, hydrating, removeOnly) {
    if (isUndef(vnode)) {
      if (isDef(oldVnode)) { invokeDestroyHook(oldVnode); }
      return
    }

    var isInitialPatch = false;
    var insertedVnodeQueue = [];

    if (isUndef(oldVnode)) {
      // empty mount (likely as component), create new root element
      isInitialPatch = true;
      createElm(vnode, insertedVnodeQueue);
    } else {
      var isRealElement = isDef(oldVnode.nodeType);
      if (!isRealElement && sameVnode(oldVnode, vnode)) {
        // patch existing root node
        patchVnode(oldVnode, vnode, insertedVnodeQueue, null, null, removeOnly);
      } else {
        if (isRealElement) {
          // mounting to a real element
          // check if this is server-rendered content and if we can perform
          // a successful hydration.
          if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {
            oldVnode.removeAttribute(SSR_ATTR);
            hydrating = true;
          }
          if (isTrue(hydrating)) {
            if (hydrate(oldVnode, vnode, insertedVnodeQueue)) {
              invokeInsertHook(vnode, insertedVnodeQueue, true);
              return oldVnode
            } else if (process.env.NODE_ENV !== 'production') {
              warn(
                'The client-side rendered virtual DOM tree is not matching ' +
                'server-rendered content. This is likely caused by incorrect ' +
                'HTML markup, for example nesting block-level elements inside ' +
                '<p>, or missing <tbody>. Bailing hydration and performing ' +
                'full client-side render.'
              );
            }
          }
          // either not server-rendered, or hydration failed.
          // create an empty node and replace it
          oldVnode = emptyNodeAt(oldVnode);
        }

        // replacing existing element
        var oldElm = oldVnode.elm;
        var parentElm = nodeOps.parentNode(oldElm);

        // create new node
        createElm(
          vnode,
          insertedVnodeQueue,
          // extremely rare edge case: do not insert if old element is in a
          // leaving transition. Only happens when combining transition +
          // keep-alive + HOCs. (#4590)
          oldElm._leaveCb ? null : parentElm,
          nodeOps.nextSibling(oldElm)
        );

        // update parent placeholder node element, recursively
        if (isDef(vnode.parent)) {
          var ancestor = vnode.parent;
          var patchable = isPatchable(vnode);
          while (ancestor) {
            for (var i = 0; i < cbs.destroy.length; ++i) {
              cbs.destroy[i](ancestor);
            }
            ancestor.elm = vnode.elm;
            if (patchable) {
              for (var i$1 = 0; i$1 < cbs.create.length; ++i$1) {
                cbs.create[i$1](emptyNode, ancestor);
              }
              // #6513
              // invoke insert hooks that may have been merged by create hooks.
              // e.g. for directives that uses the "inserted" hook.
              var insert = ancestor.data.hook.insert;
              if (insert.merged) {
                // start at index 1 to avoid re-invoking component mounted hook
                for (var i$2 = 1; i$2 < insert.fns.length; i$2++) {
                  insert.fns[i$2]();
                }
              }
            } else {
              registerRef(ancestor);
            }
            ancestor = ancestor.parent;
          }
        }

        // destroy old node
        if (isDef(parentElm)) {
          removeVnodes(parentElm, [oldVnode], 0, 0);
        } else if (isDef(oldVnode.tag)) {
          invokeDestroyHook(oldVnode);
        }
      }
    }

    invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch);
    return vnode.elm
  }

}

createElm方法里面还会对dom节点进行层级的插入。最终挂载到外层的父节点body里面,完成整个页面渲染。

分类: Web前端

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