Boolean Expressions

This page provides an overview of boolean expressions in JSON templates, including comparison operators, logical operators, truthy and falsy values. While JSON template expressions share similarities with JavaScript expressions, there are some key differences.

Comparison Operators

JSON templates support the following comparison operators:

Operator	Description	Notes
==	Equal to	No type coercion is performed with this operator
!=	Not equal to
>	Greater than	Applies to numbers, booleans, and semantic versioning
>=	Greater than or equal to	Applies to numbers, booleans, and semantic versioning
<	Less than	Applies to numbers, booleans, and semantic versioning
<=	Less than or equal to	Applies to numbers, booleans, and semantic versioning

Examples

In the following template, key evaluates to false because no type coercion is performed:

{
  "$template": {
    "key": "{{1 == '1'}}"
  }
}

In this example, key evaluates to true because the > operator applies to semantic versioning:

{
  "$template": {
    "key": "{{semver('1.0.1') > semver('1.0.0')}}"
  }
}

Logical Operators

JSON templates support these logical operators:

Operator	Description	Notes
&&	Logical AND	Short-circuiting operator; stops evaluating expressions after the first falsy expression
||	Logical OR	Short-circuiting operator; stops evaluating expressions after the first truthy expression
!	Logical NOT

Examples

In this example, the && operator stops evaluating expressions after the first falsy expression, so key evaluates to false and expensiveFunction() is not called:

{
  "$template": {
    "key": "{{false && expensiveFunction()}}"
  }
}

In this example, the || operator stops evaluating expressions after the first truthy expression, so key evaluates to true and expensiveFunction() is not called:

{
  "$template": {
    "key": "{{true || expensiveFunction()}}"
  }
}

Truthy and Falsy Values

In JSON templates, the following values are considered falsy and evaluate to false when used in a boolean expression:

• false
• 0
• null
• [] (empty array)
• {} (empty object)
• '' (empty string or a string containing only newlines and carriage returns)

All other values are considered truthy.