浅析Vue中混入mixin的实现

// 定义一个混入对象
var myMixin = {
  created: function () {
    this.hello()
  },
  methods: {
    hello: function () {
      console.log('hello from mixin!')
    }
  }
}
 
// 定义一个使用混入对象的组件
var Component = Vue.extend({
  mixins: [myMixin]
})
 
var component = new Component() // => "hello from mixin!"

var mixin = {
  data: function () {
    return {
      message: 'hello',
      foo: 'abc'
    }
  }
}
 
new Vue({
  mixins: [mixin],
  data: function () {
    return {
      message: 'goodbye',
      bar: 'def'
    }
  },
  created: function () {
    console.log(this.$data)
    // => { message: "goodbye", foo: "abc", bar: "def" }
  }
})

var mixin = {
  created: function () {
    console.log('混入对象的钩子被调用')
  }
}
 
new Vue({
  mixins: [mixin],
  created: function () {
    console.log('组件钩子被调用')
  }
})
 
// => "混入对象的钩子被调用"
// => "组件钩子被调用"

var mixin = {
  methods: {
    foo: function () {
      console.log('foo')
    },
    conflicting: function () {
      console.log('from mixin')
    }
  }
}
 
var vm = new Vue({
  mixins: [mixin],
  methods: {
    bar: function () {
      console.log('bar')
    },
    conflicting: function () {
      console.log('from self')
    }
  }
})
 
vm.foo() // => "foo"
vm.bar() // => "bar"
vm.conflicting() // => "from self"

// 为自定义的选项 'myOption' 注入一个处理器。
Vue.mixin({
  created: function () {
    var myOption = this.$options.myOption
    if (myOption) {
      console.log(myOption)
    }
  }
})
 
new Vue({
  myOption: 'hello!'
})
// => "hello!"

Vue.config.optionMergeStrategies.myOption = function (toVal, fromVal) {
  // 返回合并后的值
}

var strategies = Vue.config.optionMergeStrategies
strategies.myOption = strategies.methods

const merge = Vue.config.optionMergeStrategies.computed
Vue.config.optionMergeStrategies.vuex = function (toVal, fromVal) {
  if (!toVal) return fromVal
  if (!fromVal) return toVal
  return {
    getters: merge(toVal.getters, fromVal.getters),
    state: merge(toVal.state, fromVal.state),
    actions: merge(toVal.actions, fromVal.actions)
  }
}