What are the common properties of JavaScript?

JavaScript is a widely used programming language mainly used for web development and application development. It has many powerful properties that help developers write more flexible, efficient, and feature-rich applications. In this article, we will explore some commonly used properties in JavaScript.

1. length property

The length property is used to return the number of elements in the array. When elements are added or removed from the array, the value of this property adjusts accordingly. For example, the following code will create an array and then add three elements to it:

var myArray = [1, 2, 3];
console.log(myArray.length); // 输出3

2. prototype property

The prototype property is used to add new properties to an object and method. It is a property owned by every JavaScript object that allows programmers to add new methods to the object. For example:

function Person(name, age) {
  this.name = name;
  this.age = age;
}
Person.prototype.greet = function() {
  console.log("Hello, my name is " + this.name + " and I am " + this.age + " years old.");
}
var john = new Person("John", 25);
john.greet(); // 输出“Hello, my name is John and I am 25 years old.”

In the above code, we create a constructor called Person and add two properties (name and age) to its instance. We then added a new greet() method to the function using the prototype attribute so that every Person object can access it.

3. constructor property

The constructor property is used to return the constructor that created the object. For example:

function Person(name, age) {
  this.name = name;
  this.age = age;
}
var john = new Person("John", 25);
console.log(john.constructor); // 输出Person函数

In the above code, we created a constructor named Person and instantiated it as a john object. We then use john.constructor to check the constructor that created the john object.

4. call() method

The call() method allows us to call a function when changing the scope of an object. It calls a function using the specified this value, passing it one or more arguments. For example:

function greet() {
  console.log("Hello, my name is " + this.name + " and I am " + this.age + " years old.");
}
var john = {name: "John", age: 25};
greet.call(john); // 输出“Hello, my name is John and I am 25 years old.”

In the above code, we have created a function called greet() that uses the this variable to reference the name and age properties. Then, we create an object named john, which has a name property and an age property. Finally, we use the call() method to call the greet() function in the context of the john object.

5. apply() method

The apply() method is similar to the call() method, but it uses a parameter array to call the function. For example:

function sum(a, b) {
  console.log(a + b);
}
var values = [2, 4];
sum.apply(null, values); // 输出6

In the above code, we have created a function called sum() that adds two parameters and outputs the result to the console. We then create an array containing the two values ​​and use the apply() method to pass them to the sum() function.

6. bind() method

The bind() method creates a new function that is similar to the original function but binds the specified object and parameters. For example:

var john = {name: "John", age: 25};
function greet() {
  console.log("Hello, my name is " + this.name + " and I am " + this.age + " years old.");
}
var greetJohn = greet.bind(john);
greetJohn(); // 输出“Hello, my name is John and I am 25 years old.”

In the above code, we created an object named john and a function named greet(). Then, we use the bind() method to bind the john object and the greet() function into the greetJohn function. Finally, we call the greetJohn() function to output a welcome message.

In JavaScript, there are many other useful properties and methods available to programmers. Learning how to use them can help you write better, more flexible, and more efficient code.

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