src/core/instance/index.js

  1. function Vue (options) {
  2.   if (process.env.NODE_ENV !== 'production' &&
  3.     !(this instanceof Vue)
  4.   ) {
  5.     warn('Vue is a constructor and should be called with the `new` keyword')
  6.   }
  7.   this._init(options)
  8. }

src/core/instance/init.js

  1. Vue.prototype._init = function (options?: Object) {
  2.     const vm: Component = this
  3.     // a uid
  4.     vm._uid = uid++
  6.     let startTag, endTag
  7.     /* istanbul ignore if */
  8.     if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
  9.       startTag = `vue-perf-start:${vm._uid}`
  10.       endTag = `vue-perf-end:${vm._uid}`
  11.       mark(startTag)
  12.     }
  14.     // a flag to avoid this being observed
  15.     vm._isVue = true
  16.     // merge options
  17.     if (options && options._isComponent) {
  18.       // optimize internal component instantiation
  19.       // since dynamic options merging is pretty slow, and none of the
  20.       // internal component options needs special treatment.
  21.       initInternalComponent(vm, options)
  22.     } else {
  23.       vm.$options = mergeOptions(
  24.         resolveConstructorOptions(vm.constructor),
  25.         options || {},
  26.         vm
  27.       )
  28.     }
  29.     /* istanbul ignore else */
  30.     if (process.env.NODE_ENV !== 'production') {
  31.       initProxy(vm)
  32.     } else {
  33.       vm._renderProxy = vm
  34.     }
  35.     // expose real self
  36.     vm._self = vm
  37.     initLifecycle(vm)
  38.     initEvents(vm)
  39.     initRender(vm)
  40.     callHook(vm, 'beforeCreate')
  41.     initInjections(vm) // resolve injections before data/props
  42.     initState(vm)
  43.     initProvide(vm) // resolve provide after data/props
  44.     callHook(vm, 'created')
  46.     /* istanbul ignore if */
  47.     if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
  48.       vm._name = formatComponentName(vm, false)
  49.       mark(endTag)
  50.       measure(`vue ${vm._name} init`, startTag, endTag)
  51.     }
  53.     if (vm.$options.el) {
  54.       vm.$mount(vm.$options.el)
  55.     }
  56.   }

总结

初始化时，把不同的功能逻辑拆成单独函数，是主线逻辑一目了然。