A brief discussion on JS prototype and prototype chain

1. Prototype

All functions in JavaScript have this property, and all objects with a prototype property are functions. The purpose of prototype is to add a method/property to an object.

function persistence(){}
persion.prototype.name = "xiaoming"
console.log(persion.prototype)//{name: "xiaoming", constructor: ƒ}

2. Prototype pointer: __proto__

If the above persion function generates an instance object Persion1, and uses prototype to add an attribute to it, the writing is as follows:

function persistence(){}
persion.prototype.name = "xiaoming"
let Persion1 = new Persion();
console.log(Persion1) //The console results are as follows

The results of printing instance Persion1 are as follows:

From the results printed above, Persion1.__proto__.name = persion.prototype.name, that is, the __proto__ attribute of the instance object is equal to the prototype of its constructor.

After understanding the above, the prototype chain is easy to understand. We can directly find the Object method through Persion1.__proto__.__proto__. This may not be very intuitive, here is the code:

function persistence(){}
persion.prototype.name = "xiaoming"
let Persion1 = new Persion();
console.log(Persion1.__proto__.__proto__.toString) //The toString method of Object found through the prototype chain console.log(Object.prototype.toString) //The toString method on Object

The console prints the following results, which confirms the level-by-level search feature of the prototype chain.

Summarize

Any object can be searched level by level through the prototype chain, that is, the __proto__ attribute. The final focus is Object, and the only way is function. Their relationship is like a chain, and we call this relationship a prototype chain.

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