Conditional Logic

eSheet supports conditional rules that control field visibility, enabled state, and required state based on other field values or custom expressions.

How Rules Work

Each field can have an optional rules array. Each rule defines:

1. Effect -- What happens when the rule evaluates to true
2. Logic mode -- How multiple conditions within the rule are combined
3. Conditions -- One or more conditions to evaluate

interface ConditionalRule {
  effect: 'visible' | 'enable' | 'required';
  logic: 'AND' | 'OR';
  conditions: Condition[];
}

Effects

Effect	Behavior when rule is true	Default (no rules)
visible	Field is shown	Visible
enable	Field is interactive (not grayed out)	Enabled
required	Field must be answered	Based on required prop

Logic Modes

Mode	Behavior
AND	All conditions must be true
OR	Any condition being true is sufficient

Multiple Rules

When a field has multiple rules with the same effect, they combine with OR semantics -- if any rule evaluates to true, the effect is applied.

Condition Types

Field Conditions

Compare a target field's response against an expected value:

interface Condition {
  conditionType: 'field';
  targetId: string; // Field ID to evaluate
  operator: ConditionOperator;
  expected?: string; // Value to compare against
  propertyAccessor?: string; // Optional: 'length', 'count'
}

Expression Conditions

Evaluate a custom JavaScript-like expression:

interface Condition {
  conditionType: 'expression';
  expression: string; // e.g. '{fieldA} + {fieldB} > 100'
}

Operators

Operator	Description	Works with
equals	Exact match	Text, selection value
notEquals	Not equal	Text, selection value
contains	Text contains substring	Text answers
includes	Array includes value	Multi-select (check, ranking)
empty	Field has no answer	All field types
notEmpty	Field has an answer	All field types
greaterThan	Numeric greater than	Numeric text, rating values
greaterThanOrEqual	Numeric >=	Numeric text, rating values
lessThan	Numeric less than	Numeric text, rating values
lessThanOrEqual	Numeric <=	Numeric text, rating values

Property Accessors

Access a specific property of the target field's response before comparing:

Accessor	Description	Example use
length	Length of text answer or array	Check if multi-select has >= 3 selections
count	Number of selected items	Same as length for arrays

{
  "conditionType": "field",
  "targetId": "symptoms",
  "propertyAccessor": "length",
  "operator": "greaterThanOrEqual",
  "expected": "3"
}

Examples

Show a field when a specific option is selected

Show "Other reason" text field when the user selects "Other" in a radio:

{
  "id": "other_reason",
  "fieldType": "text",
  "question": "Please specify",
  "inputType": "string",
  "rules": [
    {
      "effect": "visible",
      "logic": "AND",
      "conditions": [
        {
          "conditionType": "field",
          "targetId": "reason",
          "operator": "equals",
          "expected": "Other"
        }
      ]
    }
  ]
}

Make a field required based on another answer

Require email when the user answers "Yes" to receiving updates:

{
  "id": "email",
  "fieldType": "text",
  "question": "Email Address",
  "inputType": "email",
  "rules": [
    {
      "effect": "required",
      "logic": "AND",
      "conditions": [
        {
          "conditionType": "field",
          "targetId": "wants_updates",
          "operator": "equals",
          "expected": "Yes"
        }
      ]
    }
  ]
}

Show field when ANY of multiple conditions are met (OR)

Show follow-up when ANY high-severity symptom is reported:

{
  "id": "followup",
  "fieldType": "longtext",
  "question": "Please describe your symptoms in detail",
  "rules": [
    {
      "effect": "visible",
      "logic": "OR",
      "conditions": [
        {
          "conditionType": "field",
          "targetId": "headache_severity",
          "operator": "equals",
          "expected": "Severe"
        },
        {
          "conditionType": "field",
          "targetId": "back_pain_severity",
          "operator": "equals",
          "expected": "Severe"
        }
      ]
    }
  ]
}

Enable based on numeric comparison

Enable a section only when the patient's age is 18 or older:

{
  "id": "adult_section",
  "fieldType": "section",
  "title": "Adult Health History",
  "rules": [
    {
      "effect": "enable",
      "logic": "AND",
      "conditions": [
        {
          "conditionType": "field",
          "targetId": "age",
          "operator": "greaterThanOrEqual",
          "expected": "18"
        }
      ]
    }
  ],
  "fields": [
    { "id": "smoker", "fieldType": "boolean", "question": "Do you smoke?" }
  ]
}

Expression-based condition

Show a BMI result field only when both weight and height have been filled:

{
  "id": "bmi_display",
  "fieldType": "display",
  "content": "Your BMI is: *<{weight} / (({height}/100) * ({height}/100))>*",
  "rules": [
    {
      "effect": "visible",
      "logic": "AND",
      "conditions": [
        {
          "conditionType": "expression",
          "expression": "{weight} > 0 && {height} > 0"
        }
      ]
    }
  ]
}

Multiple conditions with AND logic

Show a field only when BOTH conditions are met:

{
  "rules": [
    {
      "effect": "visible",
      "logic": "AND",
      "conditions": [
        {
          "conditionType": "field",
          "targetId": "has_insurance",
          "operator": "equals",
          "expected": "Yes"
        },
        {
          "conditionType": "field",
          "targetId": "insurance_type",
          "operator": "notEquals",
          "expected": "Medicare"
        }
      ]
    }
  ]
}

How Rules Are Evaluated

1. For each field, eSheet checks all rules matching the requested effect (visible, enable, or required)
2. Within a rule, conditions are combined with the rule's logic mode (AND or OR)
3. When multiple rules target the same effect, they use OR semantics -- if any rule passes, the effect is applied
4. Hidden fields (visibility = false) are excluded from validation
5. Disabled fields are excluded from validation
6. Rules are evaluated in real-time as users fill out the form