search
HomeWeb Front-endJS TutorialHow to create private variables in JavaScript?

如何在 JavaScript 中创建私有变量?

Closures, symbols, WeakMap, class private fields, and proxies are some of the techniques that can be used to create private variables in JavaScript. Each technology has advantages and disadvantages, so it is crucial to choose the one that best suits your requirements.

Like many other programming languages, JavaScript also has the concept of private variables and public variables. Private variables can only be accessed and changed by code belonging to the same scope, but public variables can be accessed and changed by any code. Let’s look at the different techniques for creating private variables in JavaScript.

Use closures

The closure method is a way to create private variables in JavaScript. A function is a closure if it can access variables defined in the scope of its parent function even after the parent function has completed and returned. We can define a variable inside a function so that it becomes private and can only be accessed by code inside that function.

Example

<html>
<body>
   <div id="demo"></div>
   <script>
      function createPrivateVariable() {
         let privateVariable = "This is a private variable";
         return {
            getValue: function () {
               return privateVariable;
            },
            setValue: function (value) {
               privateVariable = value;
            },
         };
      }
      let privateVar = createPrivateVariable();
      document.getElementById("demo").innerHTML = privateVar.getValue();
   </script>
</body>
</html>

The function createPrivateVariable in the above example returns an object with methods getValue and setValue. These methods can retrieve or change the value of the privateVariable declared in the parent function because they have access to it. If you try to access privateVariable from outside a function, a reference error occurs.

Use symbolic data types

Using symbolic data types is the second way to create private variables. Symbols can be used as property keys because they are distinct non-string identifiers. Because they are unique, external programs cannot easily access or change them.

let privateVariable = Symbol();
let obj = {
   [privateVariable]: "This is a private variable"
};
console.log(obj[privateVariable]);

Example

We can use the above code as follows -

<html>
<body>
   <div id="demo"></div>
   <script>
      let privateVar = Symbol();
      let obj = {
         [privateVar]: "This is a private variable"
      };
      Object.defineProperty(obj, 'getValue', {
         get: function() {
            return obj[privateVar];
         }
      });
      document.getElementById("demo").innerHTML = obj.getValue;
   </script>
</body>
</html>

In this example, a symbol named privateVariable has been defined and used as the object's property key. Because it is a Symbol, you cannot get the value of the property using dot notation, but you can access it through the object using square bracket notation.

Use WeakMap

WeakMaps can be used as a third way to construct private variables. The JavaScript engine only weakly references key-value pairs in a WeakMap, which allows you to link objects with keys. This makes it harder to incorrectly maintain a reference to a private variable, since the garbage collector will destroy the key-value pair if there are no other references to the key.

Example

<html>
<body>
   <div id="demo"></div>
   <script>
      let privateVariables = new WeakMap();
      let obj = {};
      privateVariables.set(obj, "This is a private variable");
      document.getElementById("demo").innerHTML = privateVariables.get(obj);
   </script>
</body>
</html>

In this example, we create a WeakMap named privateVariables to save the private variables of the object. The get() method is used to obtain a private variable after linking it to an object using the set() method. However, a private variable cannot be accessed from outside the scope formed by the object because you can access it only when you have a reference to the object.

Use object-oriented class syntax

Using object-oriented class syntax can also be used to create private variables. JavaScript’s class keyword enables us to define classes that act as templates for objects. Classes can define variables and add the # symbol before the variable name to generate private variables; this is an experimental feature and represents private variables. It is not recommended to use this feature in production code as it is not yet widely supported.

Example

<html>
<body>
   <p id="output"></p>
   <script>
      class MyClass {
         #privateVariable = "This is a private variable";
         getValue() {
            return this.#privateVariable;
         }
         setValue(value) {
            this.#privateVariable = value;
         }
      }
      let obj = new MyClass();
      document.getElementById("output").innerHTML = obj.getValue(); // "This is a private variable"
      obj.setValue("New value");
      document.getElementById("output").innerHTML = obj.getValue(); // "New value"
   </script>
</body>
</html>

In this example, a class named MyClass is constructed using private variables #privateVariable, getValue, and setValue. A reference error occurs if a method outside the class attempts to access a private variable that can only be accessed by methods inside the class.

Use proxy objects

Finally, using a Proxy object is another option for constructing private variables. Objects that can be used to intercept or change the behavior of other objects are called proxies. You can create private variables that can only be accessed by code with a proxy by encapsulating the object in a proxy.

Example

<html>
<body>
   <div id="demo"></div>
   <script>
      let privateVariable = "This is a private variable-proxy obj.";
      let handler = {
         get: function (target, name) {
            if (name === "privateVariable") {
               return privateVariable;
            }
         },
         set: function (target, name, value) {
            if (name === "privateVariable") {
               privateVariable = value;
            }
         },
      };
      let obj = new Proxy({}, handler);
      document.getElementById("demo").innerHTML = obj.privateVariable;
   </script>
</body>
</html>

In this example, a proxy with handlers with getter and setter methods has been built. These methods can retrieve or change the value of a private variable defined outside the proxy and access it. However, due to a reference error, the private variable will not be accessible from outside the proxy.

The above is the detailed content of How to create private variables in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!

Statement
This article is reproduced at:tutorialspoint. If there is any infringement, please contact admin@php.cn delete
Replace String Characters in JavaScriptReplace String Characters in JavaScriptMar 11, 2025 am 12:07 AM

Detailed explanation of JavaScript string replacement method and FAQ This article will explore two ways to replace string characters in JavaScript: internal JavaScript code and internal HTML for web pages. Replace string inside JavaScript code The most direct way is to use the replace() method: str = str.replace("find","replace"); This method replaces only the first match. To replace all matches, use a regular expression and add the global flag g: str = str.replace(/fi

Custom Google Search API Setup TutorialCustom Google Search API Setup TutorialMar 04, 2025 am 01:06 AM

This tutorial shows you how to integrate a custom Google Search API into your blog or website, offering a more refined search experience than standard WordPress theme search functions. It's surprisingly easy! You'll be able to restrict searches to y

Build Your Own AJAX Web ApplicationsBuild Your Own AJAX Web ApplicationsMar 09, 2025 am 12:11 AM

So here you are, ready to learn all about this thing called AJAX. But, what exactly is it? The term AJAX refers to a loose grouping of technologies that are used to create dynamic, interactive web content. The term AJAX, originally coined by Jesse J

Example Colors JSON FileExample Colors JSON FileMar 03, 2025 am 12:35 AM

This article series was rewritten in mid 2017 with up-to-date information and fresh examples. In this JSON example, we will look at how we can store simple values in a file using JSON format. Using the key-value pair notation, we can store any kind

10 jQuery Syntax Highlighters10 jQuery Syntax HighlightersMar 02, 2025 am 12:32 AM

Enhance Your Code Presentation: 10 Syntax Highlighters for Developers Sharing code snippets on your website or blog is a common practice for developers. Choosing the right syntax highlighter can significantly improve readability and visual appeal. T

8 Stunning jQuery Page Layout Plugins8 Stunning jQuery Page Layout PluginsMar 06, 2025 am 12:48 AM

Leverage jQuery for Effortless Web Page Layouts: 8 Essential Plugins jQuery simplifies web page layout significantly. This article highlights eight powerful jQuery plugins that streamline the process, particularly useful for manual website creation

10  JavaScript & jQuery MVC Tutorials10 JavaScript & jQuery MVC TutorialsMar 02, 2025 am 01:16 AM

This article presents a curated selection of over 10 tutorials on JavaScript and jQuery Model-View-Controller (MVC) frameworks, perfect for boosting your web development skills in the new year. These tutorials cover a range of topics, from foundatio

What is 'this' in JavaScript?What is 'this' in JavaScript?Mar 04, 2025 am 01:15 AM

Core points This in JavaScript usually refers to an object that "owns" the method, but it depends on how the function is called. When there is no current object, this refers to the global object. In a web browser, it is represented by window. When calling a function, this maintains the global object; but when calling an object constructor or any of its methods, this refers to an instance of the object. You can change the context of this using methods such as call(), apply(), and bind(). These methods call the function using the given this value and parameters. JavaScript is an excellent programming language. A few years ago, this sentence was

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment