The core competitiveness of Vue: data bidirectional binding

ZevLin 2021-05-03 11:22:50
core competitiveness vue data bidirectional

1. principle


View The changes in real time make Model change , and Model The changes can also be updated in real time to View.

Vue Using data hijacking & Release - The way subscription mode , adopt ES5 Provided Object.defineProperty() Method hijacking ( monitor ) Each attribute of getter、setter, And notify all subscribers when the data changes ( Component objects that use this property ), Trigger corresponding listening callback . To achieve Vuex Two way data binding in , It can be roughly divided into three modules :Observer、Compiler、Watcher, Pictured :


  • Observer Data listener , Responsible for monitoring all properties of data objects ( Data hijacking ), After listening to the data change, notify the subscriber .
  • Compiler Instruction parser , Responsible for scanning the template , And analyze the instructions on the template , Then bind command Events .
  • Watcher subscriber , relation Observer and Compiler. Be able to subscribe and receive notification of property changes , Execute the corresponding operation of instruction binding , Update the view . Internally implemented update() Method , Used to perform Compiler Callback bound in , Update the view .

Template parsing Watcher Will correspond to the binding instruction ( one-on-one ), This is done by calling the subscriber Watcher initialization (Watcher Medium get()) To trigger the corresponding attribute in the publisher Observer in (Object.defineProperty) Of getter,Observer Will judge whether it is through Watcher Initialize the called , If it is, it will pass Dep Class for dependency collection . Also called for the first time Watcher.update() To initialize the view . After that, every data update will pass Observer Medium setter To trigger through Dep Class collection of dependencies update Callback , Update the status in the subscriber and update the view .

Observer When dealing with objects and arrays , If it's an array , And the method called will change the length of the array , The index will be increased again and the array will be updated , Re monitoring ( Because calling array native api It will trigger many times getter、setter And the index doesn't change ). If it's an object, it's through the getter Get the value and setter Update value .

2. Version comparison

Vue It's based on two-way binding relying on mobile phones ;

3.0 Previous versions were used Object.defineProperty,3.0 The new version uses Proxy.

1) Based on data hijacking / The two-way binding advantage of dependency collection

  • Calls that don't need to be displayed ,Vue Using data to hijack + Publish subscribe , You can directly notify changes and drive views .
  • Get accurate change data directly , Hijacking attributes setter, When the attribute value changes, we can accurately get the changed content , No additional diff operation .

2)Object.defineProperty The shortcomings of

  • Can't listen to arrays , Because if the length of the array is uncertain , Monitoring will trigger it frequently getter、setter, The performance burden is too heavy (Proxy There is also the problem ).
  • Can only listen to properties , Not the whole thing , You need to traverse the properties .
  • You can only listen for property changes , Can't listen for attribute deletion .

3)Proxy The advantages of

  • Listen to the entire object without traversing properties .
  • 13 Interception methods , A lot of powerful .
  • Return the new object instead of modifying the original one , More in line with immutable.

4)Prpxy The shortcomings of

  • Poor compatibility , And it doesn't work polyfill Grinding .

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