Meet Yexp

A small expression language for querying data, transforming JSON, and putting your application’s rules into words.

Yexp combines familiar JavaScript-shaped syntax with selectors and pipelines built for data. Embed it in your application or use it from the terminal.

Start building Install Yexp and run your first expression in an app or the terminal.Learn the language Start with property access. Add filters, projections, and pipelines.

Your first expression

Suppose you have a list of products and want the names of those under $100:

{
  "products": [
    { "name": "Keyboard", "price": 75 },
    { "name": "Monitor", "price": 350 },
    { "name": "Mouse", "price": 25 }
  ]
}

Start at the input with $, select matching products, then project their names:

$.products[.price < 100][*].name
// → ["Keyboard", "Mouse"]

Prefer JavaScript-style methods? The same query can be written as:

$.products.filter(p => p.price < 100).map(p => p.name)

Try an expression in the playground →

From expression to application

Compile your expression once and evaluate it against different inputs. Yexp executes bytecode instead of using eval() or generating JavaScript.

import { compile, evaluate } from '@cristianmartinez/yexp'

const eligible = compile('$.total >= 100 && $.member')

evaluate(eligible, { total: 150, member: true }) // true
evaluate(eligible, { total: 50, member: true })  // false

The input lives at $. Pass auxiliary data explicitly through $context and $env. See Getting started for installation, runtime usage, and CLI examples.

Choose your next step

Language specification Exact semantics, built-ins, precedence, and error behavior.Under the hood Follow the path from source text to the bytecode virtual machine.

Want to see execution in motion? Step through the VM visualizer →

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