# IF/THEN Logic expressions and syntax ## Expression fundamentals The IF/THEN Logic node uses the [Navixy IoT Logic Expression Language](/docs/iot-logic-api/technologies/navixy-iot-logic-expression-language.md), which is based on Java Expression Language (JEXL). All expressions must return a boolean value (true/false) for proper node operation. **Expression evaluation**: Expressions are evaluated from left to right, and you can use parentheses to control the order of operations. **Basic syntax example**: ```jexl condition1 && (condition2 || condition3 > condition4) ``` ## Available operators ### Comparison operators

Operator	Description
`==`	Checks if two operands are equal. If operands are of different types, JEXL converts them to one if possible
`!=`	Checks for inequality of two operands. Returns true if operands are not equal
`<`	Checks that the left operand is smaller than the right operand
`<=`	Checks that the left operand is smaller or equal to the right operand
`>`	Checks that the left operand is larger than the right operand
`>=`	Checks that the left operand is larger or equal to the right operand

### Logical operators

Operator	Description
`&&` or `and`	Logical AND - checks if two conditions are true. Returns true if both conditions are true
`\|` or `or`	Logical OR - checking for the truth of at least one of the two conditions
`!` or `not`	Logical NOT - converts the result of the condition to the opposite value

### Pattern matching operators

Operator	Description
`=~`	Checks if the value of the left operand is in the set of the right operand. For strings, checks for regex pattern match
`!~`	Checks if the value of the left operand is not in the set of the right operand. For strings, checks for regex pattern mismatch
`=^`	Checks that the left string operand starts with the right string operand
`!^`	Checks that the left string operand doesn't start with the right string operand
`=$`	Checks that the left string operand ends with the right string operand
`!$`	Checks that the left string operand doesn't end with the right string operand

### Geofence functions Three functions evaluate a device's position relative to a named Navixy geofence. For usage instructions and examples, see [Geofence functions](/docs/user/guide/account/iot-logic/nodes/logic-node/geofence-functions.md).

Function	Parameter	Returns true when
`inGeofence(id)`	Geofence ID	The device is currently inside the geofence
`enterGeofence(id)`	Geofence ID	The device has just crossed into the geofence
`leaveGeofence(id)`	Geofence ID	The device has just crossed out of the geofence

**Short syntax:** ```jexl inGeofence(35229 /* Delivery zone #4 */) ``` The geofence name appears as a comment for readability and has no effect on evaluation. The geofence picker inserts this format automatically. **Long syntax** (for use with the `value()` function): ```jexl value("inGeofence(35229 /* Delivery zone #4 */)", 1, valid) ``` The second parameter is the historical index (0 for the current packet, 1 for the previous), and the third is the validity filter, following the same convention as other `value()` calls. ## Expression examples

Basic condition examples

**Equality checks**: ``` value('lock_state', 0, 'valid') == 'sealed' door_state_2 == 0 ``` **Inequality checks**: ``` value('lock_state', 1, 'valid') != 'unknown' avl_io_221 != null ``` **Numeric comparisons**: ``` value('humidity', 1, 'all') < 80 value('humidity', 1, 'all') <= 80 value('humidity', 0, 'valid') > 80 value('humidity', 0, 'valid') >= 80 ``` **Temperature monitoring**: ``` value('temperature', 0, 'valid') > 75 ``` This expression triggers when temperature exceeds 75 degrees, useful for overheating alerts. **Speed violation detection**: ``` value('speed', 0, 'valid') > 80 ``` This expression identifies when vehicles exceed 80 km/h speed limits. **Device health monitoring**: ``` value('battery_voltage', 0, 'valid') < 11.5 ``` This expression detects low battery conditions requiring maintenance attention. **Fuel level alerts**: ``` value('fuel_level', 0, 'valid') < 20 ``` This expression identifies when fuel levels drop below 20%, enabling proactive refueling.

Logical operator examples

**AND operations**: ``` value('temperature', 0, 'valid') > 15 && value('humidity', 0, 'valid') > 80 value('temperature', 0, 'valid') > 15 and value('humidity', 0, 'valid') > 80 ``` **OR operations**: ``` temperature < 10 || humidity > 80 temperature < 10 or humidity > 80 ``` **NOT operations**: ``` !condition not condition ```

Pattern matching examples

**Set membership**: ``` value('lock_state', 0, 'valid') =~ ['locked','unlocked'] value('driver_name', 0, 'valid') !~ ['John', 'Steve'] ``` **String pattern matching**: ``` driver_id =^ 'cc6f8216' driver_id !^ 'cc6f8216' value('engine_hours', 0, 'valid') =$ '1000' value('driver_id', 0, 'valid') !$ '8b38851c3c68' ```

Complex multi-condition examples

**After-hours speeding alert**: ``` value('speed', 0, 'valid') > 60 && (value('current_hour', 0, 'valid') >= 18 || value('current_hour', 0, 'valid') <= 6) ``` This combines speed monitoring with time-based conditions for enhanced safety oversight during night shifts. **Comprehensive device diagnostics**: ``` value('gps_satellites', 0, 'valid') >= 4 && value('battery_voltage', 0, 'valid') > 11.5 && value('signal_strength', 0, 'valid') > -80 ``` This validates multiple device health parameters simultaneously to ensure reliable operation. **Driver safety monitoring**: ``` value('harsh_braking', 0, 'valid') == true && value('driver_identified', 0, 'valid') == false ``` This identifies unsafe driving behavior when the driver isn't properly identified in the system. **Equipment maintenance scheduling**: ``` value('engine_hours', 0, 'valid') > 250 && value('last_maintenance', 0, 'valid') > 30 ``` This triggers maintenance alerts when engine hours exceed thresholds and maintenance is overdue. **Temperature range compliance**: ``` value('cargo_temperature', 0, 'valid') < -18 || value('cargo_temperature', 0, 'valid') > 4 ``` This detects when refrigerated cargo temperatures fall outside the acceptable range.

Expression complexity and parentheses

You can create complex expressions by combining multiple conditions with parentheses to control evaluation order: **Complex safety validation**: ``` !driver_identified && (vibration_active || speed > 3) ``` **Multi-parameter equipment check**: {% code overflow="wrap" %} ``` (value('oil_pressure', 0, 'valid') < 20 || value('coolant_temp', 0, 'valid') > 95) && value('engine_running', 0, 'valid') == true ``` {% endcode %}

## Error handling scenarios | Scenario | Result | Flow Path | Attribute Value | | ---------------------------------- | ------------------ | --------------- | --------------- | | Expression evaluates to `true` | Success | THEN connection | `true` | | Expression evaluates to `false` | Success | ELSE connection | `false` | | Referenced attribute is `null` | Treated as `false` | ELSE connection | `false` | | Syntax error in expression | Treated as `false` | ELSE connection | `null` | | Referenced attribute doesn't exist | Treated as `false` | ELSE connection | `null` | ## Practical implementation examples

Fleet temperature monitoring

**Business requirement**: Monitor refrigerated vehicles to ensure cargo temperature compliance ``` value('cargo_temperature', 0, 'valid') > 4 || value('cargo_temperature', 0, 'valid') < -18 ``` * **THEN path**: Send immediate alerts to dispatch, log compliance violations, trigger corrective actions * **ELSE path**: Continue normal processing for compliant temperatures, update status dashboards

Driver safety enforcement

**Business requirement**: Identify unsafe driving patterns during active shift hours ``` value('harsh_acceleration', 0, 'valid') == true && value('shift_active', 0, 'valid') == true ``` * **THEN path**: Generate driver coaching reports, send safety notifications, log incidents * **ELSE path**: Process normal driving behavior data, update performance metrics

Predictive maintenance alerts

**Business requirement**: Detect potential equipment failures before they occur ``` value('engine_temperature', 0, 'valid') > 95 && value('oil_pressure', 0, 'valid') < 30 ``` * **THEN path**: Schedule maintenance appointments, send technician alerts, log diagnostic data * **ELSE path**: Continue routine monitoring, update equipment health dashboards

Geofence compliance monitoring

**Business requirement**: Ensure vehicles operate within authorized areas during business hours ```jexl inGeofence(51577 /* Austin Warehouse */) && value('business_hours', 0, 'valid') == true ``` This expression uses the `inGeofence()` function to check whether a device is inside a named geofence, combined with a business-hours attribute. The geofence boundaries are managed in the Navixy geofences interface, so no coordinate values need to be maintained in the expression. * **THEN path**: Continue normal operations; device is in the authorized area during working hours. * **ELSE path**: Generate an unauthorized location alert, notify security, and log the violation. To detect the moment a vehicle leaves the authorized area rather than checking continuously, use `leaveGeofence()` instead: ```jexl leaveGeofence(51577 /* Austin Warehouse */) && value('business_hours', 0, 'valid') == true ``` For the full reference on geofence functions including `enterGeofence()` and long syntax, see [Geofence functions](/docs/user/guide/account/iot-logic/nodes/logic-node/geofence-functions.md).

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