cel-javascript

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Parser and evaluator for CEL in JavaScript using ANTLR4 This library provides parser and evaluator for Common Expression Language (CEL) expressions in Javascript and Typescript projects. CEL is a language developed by Google that allows for safe and fast evaluation of expressions in a wide variety of applications, such as policy engines, rule engines, and more.

Features

• Parse and evaluate CEL expressions directly within TypeScript projects.
• Support for common arithmetic operations, logical operations, and comparisons.
• Extensible design for adding custom functions and variables.
• Error handling during parsing with custom error listeners.
• Context-based evaluation to support dynamic expression evaluation.

Installation

Install the library via npm:

npm install @gresb/cel-javascript

Usage

Basic Example

Here is a simple example of how to use the CEL Interpreter:

import { Runtime } from 'cel-javascript';

// Define a CEL expression to evaluate
const celExpression = '1 + 2 * 3';

// Check if the expression can be parsed
if (Runtime.canParse(celExpression)) {
    // Create an instance of Runtime with the CEL expression
    const runtime = new Runtime(celExpression);

    // Evaluate the expression within a given context
    const context = "{}"; // Replace with your actual context if needed
    const result = runtime.evaluate(context);

    console.log(`Result of '${celExpression}':`, result);
} else {
    console.error('Invalid CEL expression:', celExpression);
}

Parsing Validation

You can validate if a CEL expression can be parsed without evaluating it:

import { Runtime } from '@gresb/cel-javascript';

const celExpression = '1 + 2 * 3';
const canParse = Runtime.canParse(celExpression);

console.log(`Can parse '${celExpression}':`, canParse);

Error Handling During Parsing

When parsing a CEL expression, you can catch errors and handle them accordingly:

import { Runtime } from '@gresb/cel-javascript';

const celExpression = '1 + 2 *'; // Intentional syntax error

const result = Runtime.parseString(celExpression);

if (result.success) {
    console.log('Expression parsed successfully.');
} else {
    console.error('Failed to parse expression:', result.error);
}