BonsaiSafe, typed expressions for rules, filters, and templates.

A small expression language for pricing rules, saved filters, formula fields, and user-authored logic. JavaScript syntax, checked against your data types before it runs, and bounded when it does.

Get Started

Open Playground

Read the Guide

GitHub

Familiar syntax

JavaScript operators and names. Every function is also a method, so sum(xs) and xs.sum() are the same call.

Checked before it runs

Declare your data with t and get errors for typos, wrong types, and possible nulls, with exact ranges and suggestions.

Safe by construction

No globals, prototypes, conversion hooks, or mutation. Every evaluation terminates within a step budget and size limits.

Editor support and zero dependencies

Completions, hover, and diagnostics from bonsai-js/service. Runs in Node.js, Bun, and modern browsers.

// Method chains on any value

" hello world ".trim().toUpperCase()

→ "HELLO WORLD"

// Null-safe defaults

user.profile.avatar ?? "default.png"

→ "default.png"

// "." is the current item

users.filter(.age >= 18).map(.name)

→ ["Alice"]

Use it where `eval()` would be reckless

Pricing & Eligibility

Business Rules

A pricing rule changes every quarter. With Bonsai it is a text field in your admin panel, checked against your data types when it is saved.

order.total >= freeShippingThreshold
  && customer.tier == "gold"

Search & Admin UIs

Filter Builders

Store a saved view as a string and evaluate it per row, with no custom query parser to build or maintain.

orders.filter(
  .status == "pending"
  && now() - .placedAt > days(2)
)

Notifications & Emails

Templates

Template expressions live alongside the copy, not buried in application code or a separate engine.

`Hi ${user.firstName},
  order ${order.id} ships
  ${order.shipDate.formatDate("dd MMM")}`