Let’s talk about the basic properties of JavaScript

JavaScript is an object-oriented, dynamic, weakly typed programming language. It is widely used in web development. It has good interactivity and flexibility and can be combined with HTML and CSS to develop high-quality dynamic web pages. JavaScript has the concept of attributes, which are values ​​that describe the characteristics of an object. This article will introduce the basic properties of JavaScript.

1. length property

The length property is used to get the length of a string or array. For strings, the length property returns the number of characters in the string, while for arrays, the length property returns the number of elements in the array.

For example, we can use the length attribute to get the length of a string:

var str = "hello world";
var len = str.length;
console.log(len); //输出："11"

In addition, we can also use the length attribute to get the length of an array:

var arr = [1,2,3,4,5];
var len = arr.length;
console.log(len); //输出："5"

2. prototype property

The prototype property is a unique property of the function object. It is a pointer to the prototype object. Every JavaScript function has a prototype attribute, whether it is a built-in function or a custom function.

For example, we can define a Person function and define a sayHello method in its prototype attribute:

function Person(name) {
  this.name = name;
}

Person.prototype.sayHello = function() {
  console.log("Hello, my name is " + this.name);
}

Then, we can create a Person instance and call the sayHello method:

var person = new Person("John");
person.sayHello(); //输出："Hello, my name is John"

3. constructor attribute

The constructor attribute is a reference to the constructor function. When we create an object, it automatically adds a constructor attribute pointing to the constructor that created the object.

For example, we can create an object with a custom constructor and get its constructor property:

function Car(make, model) {
  this.make = make;
  this.model = model;
}

var myCar = new Car("Toyota", "Camry");
console.log(myCar.constructor); //输出：Car(make, model)

4. toString() method

## The #toString() method is a method used to return a string representation of an object. It converts an object to string type and back.

For example, we can use the toString() method to convert a numeric type object into a string type:

var num = new Number(10);
var str = num.toString();
console.log(str); //输出："10"

valueOf() method
5. ## The #valueOf() method is a method used to return the original value of an object. It converts an object to a primitive type and back.

For example, we can use the valueOf() method to convert a numeric type object into a primitive numeric type:

var num = new Number(10);
var val = num.valueOf();
console.log(val); //输出：10

Object.prototype property

6. ## The #Object.prototype property is the ancestor of all JavaScript objects (including function objects). The Object.prototype property can be accessed directly. It is an object and contains some basic methods and properties.

For example, we can use the Object.prototype.toString() method to return a string representation of an object:

var obj = {name:"John", age:30};
var str = Object.prototype.toString.call(obj);
console.log(str); //输出："[object Object]"

Summary

In JavaScript, a property is a A value that describes an object's properties. Common JavaScript basic properties include: length, prototype, constructor, toString() method, valueOf() method and Object.prototype property, etc. Mastering these properties is very helpful for in-depth understanding of the basics of the JavaScript language.

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