Skip to content

Latest commit

 

History

History
71 lines (57 loc) · 3.34 KB

Function与Object.md

File metadata and controls

71 lines (57 loc) · 3.34 KB

Function and Object

In JavaScript, there are two top-level objects Function and Object. Object is the base class of all objects, and all constructor functions are instances of the Function object at the same time.

Object

All objects in JavaScript are derived from Object. All objects inherit methods and properties from Object.prototype, although they may be overridden, for example, other constructor functions implement their own toString() method in the prototype. Changes to the Object prototype object will propagate to all objects unless these overridden properties and methods along the prototype chain are modified.

// Define three objects
var a = function(){} // constructor function object
var b = new Array(1); // array object
var c = new Number(1); // number object // wrapper object

// Check the prototype chain
console.log(a.__proto__.__proto__ === Object.prototype); // true
console.log(b.__proto__.__proto__ === Object.prototype); // true
console.log(c.__proto__.__proto__ === Object.prototype); // true

// Split the references
console.log(a.__proto__ === Function.prototype); // true
console.log(Function.prototype.__proto__ === Object.prototype); // true
console.log(b.__proto__ === Array.prototype); // true
console.log(Array.prototype.__proto__ === Object.prototype); // true
console.log(c.__proto__ === Number.prototype); // true
console.log(Number.prototype.__proto__ === Object.prototype); // true

// Using instanceof is actually checking the prototype chain
// The instanceof operator checks whether the prototype property of a constructor appears in the prototype chain of an instance object
console.log(a instanceof Object); // true
console.log(b instanceof Object); // true
console.log(c instanceof Object); // true

Function

All constructor functions in JavaScript inherit from Function, including the Object constructor function. The Function constructor function also inherits from itself, and of course, Function also inherits from Object.prototype, it can be said that the Object.prototype existed first, and Object.prototype constructed Function.prototype, and then Function.prototype constructed Object and Function.

// Constructor function object
var a = function(){} // constructor function object

// Check the prototype chain
console.log(a.__proto__ === Function.prototype); // true
console.log(Object.__proto__ === Function.prototype); // true
console.log(Function.__proto__ === Function.prototype); // true
console.log(Function.prototype.__proto__ === Object.prototype); // true

// Using instanceof 
console.log(a instanceof Function); // true
console.log(Object instanceof Function); // true
console.log(Function instanceof Function); // true

Summary

  • All objects inherit from Object, and inherit methods and properties from Object.prototype.
  • All constructor functions, including Object and Function, inherit from Function, and ultimately inherit from Object.

Daily Question

https://github.com/WindrunnerMax/EveryDay

References

https://www.cnblogs.com/tiancai/p/7463252.html
https://www.cnblogs.com/yf2196717/p/10989466.html
https://www.cnblogs.com/ioveNature/p/6880176.html
https://www.cnblogs.com/tiffanybear/p/11320651.html
https://blog.csdn.net/backee/article/details/83378772
https://blog.csdn.net/weixin_34237596/article/details/88026745