Evalis

A secure, user-friendly expression evaluator for TypeScript and JavaScript.

Early Release: This is an early release with core functionality. More features are in active development. Check the main project for roadmap and updates.

Installation

npm install evalis

Quick Start

import { evaluateExpression } from 'evalis';

const context = { a: { b: 5 } };
const value = evaluateExpression('a.b + 2', context);

console.log(value); // 7

Features

• Safe evaluation - No eval(). No access to global namespace.
• Simple syntax - Familiar expressions with property access, operators, and comprehensions.
• Type-safe - Full TypeScript support with type definitions included.

Supported Operations

• Arithmetic: +, -, *, /
• Comparison: ==, !=, <, <=, >, >=
• Logical: and, or, not
• Property access: obj.property, obj['key']
• Array access: arr[0]
• List comprehensions: [x * 2 for x in numbers]
• Membership: x in collection
• String literals: Both 'single' and "double" quotes supported

Note on + operator:

• Numbers: 5 + 3 → 8
• Strings: "hello" + "world" → "helloworld" (coerces primitives to string)
• Arrays: [1, 2] + [3, 4] → [1, 2, 3, 4]
• Mixed types (array + string) will throw EvalisError

More Information

This is the TypeScript/JavaScript implementation of Evalis. For more details about the project:

• Main Project
• Architecture
• Python Implementation

License

MIT