Expressions

The Builder and DevCore framework use JavaScript-like expressions throughout the system to provide flexible control over processing logic and application UI behavior. These expressions enable dynamic configuration and conditional logic without requiring code changes.

Expression Usage

Expressions are used in the following contexts:

UI Control

• View.enable - Enable or disable specific views based on conditions
• Widget.show - Control widget visibility dynamically

System Logic

• Software Update Policy - Determine if updates should be applied to specific devices
• Automated Actions - Control conditional logic in if/then/else statements

Expression Context

Expressions are JavaScript-style statements that resolve to boolean results. They have access to context variables that vary depending on the usage context.

Context Variables

The following variables are available in expression contexts:

Variable	Type	Description	Context
agent	String	Browser user agent string	UI contexts
dark	Boolean	True if in dark mode	UI contexts
design	Boolean	True if widget is in design mode	Widget contexts
desktop	Boolean	True if running on desktop (not mobile)	UI contexts
framed	Boolean	True if board is framing widgets	Widget contexts
height	Number	Browser height dimension (window.innerHeight)	UI contexts
language	String	Browser language setting (navigator.language)	UI contexts
light	Boolean	True if in light mode	UI contexts
mobile	Boolean	True if running on mobile device (≤ 640px width)	UI contexts
value	Various	Widget data or input value	Widget contexts
width	Number	Browser width dimension (window.innerWidth)	UI contexts

Expression Examples

Basic Conditions

// Simple value comparison
value > 0
value == "active"
value != null

// Boolean conditions
dark && mobile
light || desktop

Device-Based Conditions

// Screen size conditions
width < 640                    // Mobile devices
width >= 640 && width <= 1024  // Tablet devices
width > 1024                   // Desktop devices

// Combined device conditions
mobile && language == "en"     // English mobile users
desktop && !dark              // Desktop light mode

String Operations

// String matching
agent ^= "Chrome"             // User agent starts with "Chrome"
language $= "US"              // Language ends with "US"
value >< "error"              // Value contains "error"

// Regular expressions
agent =~ /Chrome|Firefox/     // Chrome or Firefox browsers
language =~ /^en/             // English language variants

Expression Operators

Arithmetic Operators

+ - * / % ^ ( )

Comparison Operators

== != < <= > >=

Logical Operators

&& || !

String Operators

Operator	Description
^=	Starts with
^!=	Does not start with
$=	Ends with
$!=	Does not end with
><	Contains
<>	Does not contain

Regular Expression Support

Regular expressions (delimited by slashes) can be used with equality operators:

agent =~ /Mobile/              // Mobile user agent
value =~ /^[0-9]+$/           // Numeric values only

Expression Limitations

Performance Constraints

• Term Limit - Maximum of 50 terms per expression
• Runtime Protection - Prevents denial of service attacks
• Evaluation Timeout - Expressions must complete within reasonable time

Type Support

The expression engine supports:

• Numbers (integers and floating-point)
• Boolean values (true/false)
• String literals (quoted strings)
• Regular expressions (slash-delimited)
• Null values

Best Practices

Performance Optimization

• Keep expressions simple and focused
• Avoid complex nested conditions when possible
• Use appropriate operators for string comparisons
• Test expressions with expected data ranges

Maintainability

• Document complex expressions clearly
• Use descriptive variable names in context
• Group related conditions with parentheses
• Avoid overly complex regular expressions

Security Considerations

• Validate expression inputs where possible
• Be aware of term limits for complex expressions
• Consider performance impact of frequent evaluations

Common Use Cases

Responsive Design

// Show widget only on desktop
desktop && width > 1024

// Hide widget on mobile
!mobile

Feature Toggles

// Enable feature for specific language
language == "en" || language == "fr"

// Show advanced features for power users
value == "admin" || value == "power"

Conditional Updates

// Update policy for production devices
value.environment == "production" && value.version < "2.0"

// Emergency updates only
value.priority == "critical"

Debugging Expressions

Testing Approaches

• Use simple test cases to validate logic
• Test with different context variable values
• Verify boolean results match expectations
• Check for edge cases with null or undefined values

Common Issues

• Incorrect operator precedence
• Missing parentheses in complex conditions
• Type mismatches in comparisons
• Regular expression syntax errors