> ## Documentation Index
> Fetch the complete documentation index at: https://docs.js-confuser.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Countermeasures

> A custom callback function to invoke when a lock is triggered.

* Option name: `"lock.countermeasures"`

* Option value: `string`

***

### Input / Output

This example showcases how `Countermeasures` transforms the code. Try it out by changing the input code and see changes apply in real-time.

```js title="Input.js" lines interactive-mode="obfuscate" theme={null}
// Input.js
function onTamperDetected() {
  throw new Error('The code has been tampered with!');
}

// Output.js
var NY0SMF = !1;
function gy78un() {
  if (NY0SMF) return;
  NY0SMF = !0;
  oGq6X3v();
}
function oGq6X3v() {
  throw new Error('The code has been tampered with!');
}
```

***

### Crash Process

The default behavior is to crash the process This is done by an infinite loop to ensure the process becomes useless.

```js lines theme={null}
while(true) {
  // ...
}
```

### Custom Callback

By setting countermeasures to a string, it can point to a callback to invoke when a lock is triggered. The countermeasures callback function can either be a local name or an external name.

Examples:

* `"onLockTriggered"`
* `"window.onLockTriggered"`

If the function is defined within the locked code, it must follow the local name rules.

### Local Name rules

1. The function must be defined at the top-level of your program.
2. The function must not rely on any scoped variables.
3. The function cannot call functions outside it's context.

These rules are necessary to prevent an infinite loop from occurring.

### Test your countermeasure

#### Domain Lock:

Try your code within DevTools while on another website.

#### Time Lock:

Try setting your machine time to before or past the allowed range.

#### Integrity:

Try changing a string within your code.

***

### Usage Example

The provided code example will obfuscate the file `input.js` and write the output to a file named `output.js`.

```js title="Usage Example" lines theme={null}
import JSConfuser from "js-confuser";
import {readFileSync, writeFileSync} from "fs";

// Read input code
const sourceCode = readFileSync("input.js", "utf8");
const options = {
  target: 'browser',
  lock: {
    countermeasures: 'onTamperDetected',
  },
};

JSConfuser.obfuscate(sourceCode, options).then((result)=>{
  // Write output code
  writeFileSync("output.js", result.code);
}).catch(err=>{
  // Error occurred
  console.error(err);  
});
```

***

#### Enabled In

* [High Preset](/presets/high): No
* [Medium Preset](/presets/medium): No
* [Low Preset](/presets/low): No

***

#### See Also

* [Integrity](./integrity)
* [Tamper Protection](./tamperProtection)