Vuecomputed实现原理深入讲解

<template>
  <div>
    {{getA}}
    <button @click="addModule">新增</button>
  </div>
</template>
<script>
export default {
  name: "TestwebpackTest",
  mounted() {
    console.log(this);
  },
  data() {
    return {
      num: 1,
      a:2
    };
  },
  computed:{
    getA(){
      return this.a
    }
  },  
  methods: {
    addModule() {
      this.a++;
    }
  }
};
</script>
<style lang="sCSS">
div {
  .test {
    width: 10px;
    height: 15px;
    background-color: blue;
  }
}
</style>

Vue.extend = function (extendOptions) {
    ...
    if (Sub.options.computed) {
        initComputed(Sub);
    }
    ...
};

function initComputed(Comp) {
    var computed = Comp.options.computed;
    for (var key in computed) {
        defineComputed(Comp.prototype, key, computed[key]);
    }
}

var sharedPropertyDefinition = {
      enumerable: true,
      configurable: true,
      get: noop,
      set: noop
  };
// key: "getA"  target: Vue {constructor: ƒ} userDef:ƒ getA()
function defineComputed(target, key, userDef) {
      var shouldCache = !isServerRendering(); // true
      if (isFunction(userDef)) {
          sharedPropertyDefinition.get = shouldCache
              ? createComputedGetter(key)
              : createGetterInvoker(userDef);
          sharedPropertyDefinition.set = noop;
      }
      else {
         ...
      }
     ...
      Object.defineProperty(target, key, sharedPropertyDefinition);
  }

// key: "getA"
function createComputedGetter(key) {
      return function computedGetter() {
          var watcher = this._computedWatchers && this._computedWatchers[key];
          if (watcher) {
              if (watcher.dirty) {
                  watcher.evaluate();
              }
              if (Dep.target) {
                  if (Dep.target.onTrack) {
                      Dep.target.onTrack({
                          effect: Dep.target,
                          target: this,
                          type: "get" ,
                          key: key
                      });
                  }
                  watcher.depend();
              }
              return watcher.value;
          }
      };
  }

var render = function render() {
  var _vm = this,
    _c = _vm._self._c
  return _c("div", [
    _vm._v("\n  " + _vm._s(_vm.getA) + "\n  "),
    _c("button", { on: { click: _vm.addModule } }, [_vm._v("新增")]),
  ])
}

var watcher = this._computedWatchers && this._computedWatchers[key];
 if (watcher) {
     if (watcher.dirty) { // true
         watcher.evaluate();
     }
     if (Dep.target) {
         if (Dep.target.onTrack) {
             Dep.target.onTrack({
                 effect: Dep.target,
                 target: this,
                 type: "get" ,
                 key: key
             });
         }
         watcher.depend();
     }
     return watcher.value;
 }
Watcher.prototype.evaluate = function () {
     this.value = this.get();
     this.dirty = false;
 };

Watcher.prototype.get = function () {
     pushTarget(this);
     var value;
     var vm = this.vm;
     try {
         value = this.getter.call(vm, vm);
     }
     catch (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;
 };

var value = getter ? getter.call(obj) : val;
if (Dep.target) {
     {
         dep.depend({
             target: obj,
             type: "get" ,
             key: key
         });
     }
     ...
 }
 return isRef(value) && !shallow ? value.value : value;
 ...
Dep.prototype.depend = function (info) {
   if (Dep.target) {
        Dep.target.aDDDep(this);
        if (info && Dep.target.onTrack) {
            Dep.target.onTrack(__assign({ effect: Dep.target }, info));
        }
    }
};
...
Watcher.prototype.addDep = function (dep) {
    var id = dep.id;
    if (!this.newDepIds.has(id)) {
        this.newDepIds.add(id);
        this.newDeps.push(dep);
        if (!this.depIds.has(id)) {
            dep.addSub(this);
        }
    }
};

function ReactiveSetter(newVal) {
    var value = getter ? getter.call(obj) : val;
     ...
     else if (!shallow && isRef(value) && !isRef(newVal)) {
         value.value = newVal;
         return;
     }
     else {
         val = newVal;
     }
     childOb = !shallow && observe(newVal, false, mock);
     {
         dep.notify({
             type: "set" ,
             target: obj,
             key: key,
             newValue: newVal,
             oldValue: value
         });
     }
 }

Dep.prototype.notify = function (info) {
    // stabilize the subscriber list first
    var subs = this.subs.slice();
    ...
    for (var i = 0, l = subs.length; i < l; i++) {
        ...
        subs[i].update();
    }
};
Watcher.prototype.update = function () {
   
    if (this.lazy) {
        this.dirty = true;
    }
    else if (this.sync) {
        this.run();
    }
    else {
        queueWatcher(this);
    }
};