Prototype chain analysis

What is prototype chain

Objects have prototype objects （ The prototype object is described below ）, Prototype objects have prototype objects , It forms a chain structure , It's called the prototype chain . The figure below is a partial structure of the prototype chain （ You can customize the person Constructor looks like ）.
person Constructor through new person() Create examples P1,p1 Can pass -proto- Access its prototype object , Constructors can be constructed by prototype Property to access the prototype object , Prototype objects can also be created by constructor Access the constructor .
As object , The prototype object also has its prototype object （ Because all objects have prototype objects ）, So you can also pass -proto- Access his prototype object , Here it is. Object, and Object The prototype object of is null.

The role of the prototype chain

For member lookup
When accessing members of an object , It is impossible to find whether the prototype object that will access it has this member
, Keep looking along the prototype chain , Know they're found , If it is not found, it will return undefined.

The role of prototype objects

stay ES5 front , Object - oriented programming is implemented through constructors and prototype objects , Using constructors has one drawback —— Objects created using constructors do not use the same method , It's a waste of memory . How to make these objects use the same method ？ At this point, the prototype object will be used .
Every object can use prototype Property to access the prototype object , Members added to the prototype object can be accessed by the instance object created by the constructor .