Expression language syntax

There are three types of expressions supported:

JSON Path Expressions

When the expression starts with $, it is treated as a JSON Path expression and will be evaluated as such.

JSON Path Syntax

JSON Path	Description
`$`	The root object
`.`	Child operator
`@`	The current object
`*`	Wildcard. All elements in an array, or all properties of an object
`..`	Recursive descent
`[]`	Subscript operator
`[,]`	Union operator
`[start : end : step]`	Array slice operator
`?(expression)`	Filter expression
`()`	Script expression

Examples:

// Given the context: { user: { name: "John", age: 30 }, "info/email": "[email protected]" }
'$.user.name'         // Returns "John"
'$.user.age'          // Returns 30
'$.user[*]'           // Returns ["John", 30]
'$["info/email"]'     // Returns "[email protected]"

For more information on JSON Path syntax, refer to the original JSON Path documentation.

JEXL Expressions

This kind of expression is enclosed in double brackets {{expression}}. It supports variables and operators.

Operators

Operator	Description
`!`	Logical NOT
`+`	Addition, string concatenation
`-`	Subtraction
`*`	Multiplication
`/`	Division
`//`	Floor division
`%`	Modulus
`^`	Exponentiation
`&&`	Logical AND
`	\|`	Logical OR
`==`	Equal
`!=`	Not equal
`>`	Greater than
`>=`	Greater than or equal
`<`	Less than
`<=`	Less than or equal
`in`	Element of string or array
`? :`	Ternary operator

Examples:

// Given the context: { x: 10, y: 5 }
'{{x + y}}'                  // Returns 15
'{{x * 2}}'                  // Returns 20
'{{x > y}}'                  // Returns true
'{{x == 10 ? "yes" : "no"}}' // Returns "yes"
'{{x in [1, 2, 3]}}'         // Returns false
'{{x != y}}'                 // Returns true

Identifiers

Identifiers can be used to reference variables in the context.

// Given the context:
// { 
//     name: {
//         first: "John",
//         last: "Smith"
//     },
//     jobs: ["Developer", "Designer"]
// }
`{{name.first}}`          // Returns "John"
`{{jobs[1]}}`             // Returns "Designer"

Collections

Collections, or arrays of objects, can be filtered by including a filter expression in brackets.

// Given the context:
// {
//     users: [
//         { name: "John", age: 30 },
//         { name: "Jane", age: 25 }
//     ]
// }
`{{users[.name == "John"].age}}` // Returns 30
`{{users[.age > 25].name}}`      // Returns ["John"]

String Interpolation

To simplify strings usage, a more straightforward syntax is provided for string interpolation of variables using the ${var} syntax.

Examples:

// Given the context: { name: "John", age: 30 }
"Hello ${name}"       // Returns "Hello John"
"User is ${age}"    // Returns "User is 30"

Note: If the expression is a string without any of the patterns described above, it will be returned as is.

// Given the context: { name: "John", age: 30 }
"Hello world"       // Returns "Hello world"

For more information on the JEXL syntax, refer to the JEXL Syntax documentation.