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JSDefender Demo

Free Online JavaScript Obfuscator—Powered by JSDefender

JavaScript code is readable by default—anyone who opens their browser's dev tools can inspect, copy, or reverse-engineer your application logic. This free online obfuscator, powered by JSDefender, lets you see exactly how PreEmptive protects your JavaScript from reverse engineering, tampering, and theft.
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Paste or upload any JavaScript below, select protection options and click Protect to see the online obfuscator in action:
By evaluating and using this tool, the user agrees to the terms of use.

What makes PreEmptive different?

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While other online obfuscators provide basic functionality, PreEmptive offers:

  • Professional-grade in-app obfuscation for JavaScript
  • Fully on-premise—your code stays secure without relying on external servers
  • Real-world-tested transformations used by enterprise and commercial software providers
  • Seamless integration with PreEmptive’s other protection tools for .NET, MAUI, Android, and more.
layered obfuscation

Full list of JSDefender protection transforms

JSDefender applies multiple layers of transformation to your JavaScript, making it significantly harder to read, reverse engineer, or tamper with—while preserving full functionality for your users.

Control Flow Protection

Restructures execution paths by injecting opaque predicates, dead code, and flattened logic — making the program's flow nearly impossible to follow statically

Boolean Literals

Replaces true and false literals with equivalent expressions that are harder to recognize and analyze

Integer Literals

Replaces numeric literals with equivalent expressions, optionally converting values to a different radix (binary, hex, octal) to obscure their meaning

Expression Sequence Obfuscation

Merges adjacent statements into chained expression sequences that are significantly harder to read and parse

Variable Grouping Protection

Separates variable declarations from their initializations and relocates the declaration to the end of its scope to obscure data flow

Local Declaration

Mangles the names of local variables and declarations so their purpose cannot be inferred

Property Indirection

Converts direct property access into indirect access, hiding object structure from static analysis

Property Sparsing

Breaks object literal assignments into separate statements to obscure data structure and intent

Function Reordering

Relocates functions away from their original positions within the same lexical scope, disrupting readability and analysis

String Literals

Extracts string literals into variables initialized from encoded values, hiding readable text such as messages, endpoints, and keys from plain view

Debugger Removal

Strips debugging artifacts and metadata from production code that could otherwise help an attacker inspect or step through your application

Tamper Detection

Wraps critical code sections in runtime guards that detect unauthorized modifications — tampered code will not execute correctly

Domain Lock

Binds your code to one or more approved domains; execution breaks with an error if the code runs from an unauthorized origin

Date Lock

Restricts code execution to a defined time window — code running outside that window can exit silently or trigger a custom response

Frequently Asked Questions

JavaScript obfuscation transforms readable JavaScript into code that is much harder to understand and analyze. It is designed to preserve functionality while raising the effort required to reverse engineer logic or copy IP. JSDefender protects JavaScript using multiple transformation and injection techniques.

JSDefender is designed to help prevent reverse engineering, tampering, and unauthorized debugging. Because JavaScript ships in source form, attackers can inspect code directly in browsers and runtimes. JSDefender includes techniques like DevTools blocking, debugger statement removal, and tamper-resistant protections to make these attacks harder.

Yes. JSDefender supports React, Angular, Vue, Node.js, and most major JavaScript frameworks. Many teams choose to focus protection on IP-sensitive application code rather than every third-party module, and JSDefender supports partial protection to make that possible.

Yes. JSDefender supports partial protection using inline configuration directives in the source code, combined with external configuration. This lets you apply different protections to different parts of the codebase and exclude code you do not want to protect.

You can run JSDefender from the command line using the JSDefender CLI, or integrate it into bundlers.

Domain locking locks protected code to a specified URL or domain. Date locking allows code to run within a specific date interval, which can be especially useful for trials or beta periods. Both can be configured by command line interface or configuration file.

Yes. There is a free trial for JSDefender, and there is also an online JavaScript obfuscator demo you can use to preview how protections affect code output

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You’ve seen the power of JSDefender for yourself—now it’s time to protect your whole app.

Try the full-featured version of JSDefender for free.
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