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" /* TrackOpTypes.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" /* TrackOpTypes.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" /* TrackOpTypes.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" /* TriggerOpTypes.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 () {
/* istanbul ignore else */
if (this.lazy) {
this.dirty = true;
}
else if (this.sync) {
this.run();
}
else {
queueWatcher(this);
}
};