Vuewatch原理源码层深入讲解

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

function initState(vm) {
var opts = vm.$options;
...
if (opts.watch && opts.watch !== nativeWatch) {
initWatch(vm, opts.watch);
}
}
...
function initWatch(vm, watch) {
for (var key in watch) {
var handler = watch[key];
if (isArray(handler)) {
for (var i = 0; i < handler.length; i++) {
createWatcher(vm, key, handler[i]);
}
}
else {
createWatcher(vm, key, handler);
}
}
}
...
function createWatcher(vm, expOrFn, handler, options) {
if (isPlainObject(handler)) {
options = handler;
handler = handler.handler;
}
if (typeof handler === 'string') {
handler = vm[handler];
}
return vm.$watch(expOrFn, handler, options);
}

Vue.prototype.$watch = function (expOrFn, cb, options) {
var vm = this;
...
options = options || {};
options.user = true;
var watcher = new Watcher(vm, expOrFn, cb, options);
...
return function unwatchFn() {
watcher.teardown();
};
};

function Watcher(vm, expOrFn, cb, options, isRenderWatcher) {
...
this.dirty = this.lazy; // for lazy watchers
this.deps = [];
this.newDeps = [];
...
// expOrFn = 'a'
if (isFunction(expOrFn)) {
this.getter = expOrFn;
}
else {
this.getter = parsePath(expOrFn);
...
}
this.value = this.lazy ? undefined : this.get();
}

function parsePath(path) {
...
// ['a']
var segments = path.split('.');
return function (obj) {
for (var i = 0; i < segments.length; i++) {
if (!obj)
return;
obj = obj[segments[i]];
}
return obj;
};
}

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

// obj = 'vm' segments = ['a']
function (obj) {
for (var i = 0; i < segments.length; i++) {
if (!obj)
return;
obj = obj[segments[i]];
}
return obj;
}

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++) {
if (info) {
var sub = subs[i];
sub.onTrigger &&
sub.onTrigger(__assign({ effect: subs[i] }, info));
}
subs[i].update();
}
};
Watcher.prototype.update = function () {
// this.lazy = false
if (this.lazy) {
this.dirty = true;
}
...
else {
queueWatcher(this);
}
};

Watcher.prototype.run = function () {
if (this.active) {
var value = this.get();
if (value !== this.value ||
// Deep watchers and watchers on Object/Arrays should fire even
// when the value is the same, because the value may
// have mutated.
isObject(value) ||
this.deep) {
// set new value
var oldValue = this.value;
this.value = value;
if (this.user) {
var info = "callback for watcher \"".concat(this.expression, "\"");
// this.cb是watch方法a的函数
invokeWithErrorHandling(this.cb, this.vm, [value, oldValue], this.vm, info);
}
else {
this.cb.call(this.vm, value, oldValue);
}
}
}
};

function invokeWithErrorHandling(handler, context, args, vm, info) {
var res;
try {
res = args ? handler.apply(context, args) : handler.call(context);
if (res && !res._isVue && isPromise(res) && !res._handled) {
res.catch(function (e) { return handleError(e, vm, info + " (Promise/async)"); });
res._handled = true;
}
}
catch (e) {
handleError(e, vm, info);
}
return res;
}