Dynamic JavaScript injection from external systems is not allowed in Salesforce. To ensure security, follow these best practices:
**Core Security Requirements:**
- Host JavaScript statically within the Salesforce environment, such as in static resources
- Avoid dynamically loading JavaScript from external domains or third-party servers, as this can lead to vulnerabilities like code injection or unauthorized access
- Do not dynamically load JavaScript from external domains, even if trusted, as this is not permitted due to security risks
**Implementation Guidelines:**
1. **Use Static Resources**: Store JavaScript files in static resources within your Salesforce package to ensure version control and security review
2. **Include Scripts Securely**: Use the `<apex:includeScript>` tag to load JavaScript from static resources in Visualforce pages:
```html
<apex:includeScript value="{{! $Resource.YourJavaScriptFile }}"/>
```
3. **Document API Callouts**: If the script interacts with external systems, document all API callouts and ensure they are reviewed during the security process
4. **Consider Isolation**: If external hosting is unavoidable, embed the script in an iframe to isolate it from the Salesforce domain
**Additional Security Measures:**
- Follow secure coding guidelines and avoid using JSONP
- Document your use case thoroughly and consult with the security review team for specific implementations
- Ensure compliance with Salesforce security standards to protect against vulnerabilities
These practices help maintain the security integrity of your Salesforce environment while enabling necessary functionality.