JEXL Language Guide

JEXL (JavaScript Expression Language) is a powerful expression language for evaluating expressions within JSON structures and JavaScript applications. This guide covers the complete JEXL syntax and language features.

What is JEXL?

JEXL provides a simple, yet powerful syntax for:

• Data transformation - Transform objects and arrays
• Filtering - Select data based on conditions
• Calculations - Perform mathematical operations
• String manipulation - Process and format text
• Conditional logic - Make decisions in expressions

Language Sections

Syntax Overview

Learn the basic JEXL syntax, expression structure, and evaluation rules.

Data Types

Understand JEXL's data types: strings, numbers, booleans, arrays, objects, and null.

Operators

Complete reference for all JEXL operators including arithmetic, comparison, logical, and more.

Expressions

Learn how to write complex expressions using functions, transforms, and nested operations.

Context and Variables

Understand how JEXL accesses data through context variables and property paths.

Quick Examples

Basic Expression

// Simple property access
name
// Returns the 'name' property from context

Array Operations

// Filter and transform array
users|filter("value.age > 21")|map("value.name")
// Filters users by age, then extracts names

Mathematical Calculations

// Calculate percentage
(score / maxScore) * 100
// Calculates percentage from score and maxScore

String Processing

// Clean and format text
title | trim | lowercase | replace(" ", "-")
// Cleans title and converts to slug format

Conditional Logic

// Conditional expression
age >= 18 ? "adult" : "minor"
// Returns status based on age

Key Concepts

Expressions vs Statements

JEXL uses expressions that always return a value, not statements. Every JEXL expression evaluates to a result.

Context-Driven

JEXL expressions are evaluated against a context - a JavaScript object that provides the data for the expression.

Functional Style

JEXL encourages a functional programming style with transforms (pipe operations) that chain data transformations.

Type Flexibility

JEXL handles JavaScript's dynamic typing, automatically converting between types when needed.

Getting Started

1. Start with Syntax - Learn the basic JEXL syntax
2. Explore Data Types - Understand how JEXL handles different data types
3. Master Operators - Learn all available operators
4. Practice Expressions - Build complex expressions
5. Understand Context - Learn how data flows through expressions

Ready to dive in? Start with the Syntax Overview!