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Javascript library for evaluation of functional expressions
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NPM version Build Status Dependency Status Coverage Status


A Javascript api for evaluating functional expressions.

Example usage:

// compile the expression into a function   
var fn = funex("");

// Evaluate the expression with a scope
var result = fn({person: {name: {first: "John", last: "Doe"}}});

// Would output "JOHN"


This library bring the concept of a funex, which is short for "Functional Expressions".

Functionnal expressions is a subset of javascript that only the simplest parts while still being usefull. It mosty allows function calls, property access, numbers, strings, JSON and a few other tricks.

By being so simple and so specific, it allows you to use dynamic expressions in a context that need to be controlled and secure.

In other words, it's similare to "eval", without being "evil".


  • Secure: Expressions are evaluated and executed in a controlled and secure scope
  • Supports function calls, dot notation, array/object members, strings, numbers, JSON syntax
  • Provide simple objects or use array of objects to simulate closures.
  • The syntax is a familiar subset of javascript
  • Simple because it is logic-less: no operators, statements or boolean logic.
  • Runs both in browser and on the server
  • No complex api or configuration, it is a single function to use

Usefull for ...

  • Resolving richer but secure expressions in templating engines
  • A good replacement for some uses of .eval()
  • Scenarios where third parties can customize portion of your apps without compromising security
  • To allow secure macros in extendable apps
  • For computable values in configs

Funex is also awesome because ...

  • Small : Minified + Gzipped source is around 1.5k
  • Compiled expressions can be cached and reused
  • Throws readable syntax errors
  • Minimal overhead compared to native code
  • Extensive test suite with 100% coverage - Coverage Status
  • Public Domain code maintained on Github
  • Source code is short, documented and low in complexity - doc/plato/index.html
  • Has specific builds for browsers, node.js and AMD and is deployed to Travic CI - Build Status

Installation on Node.js

npm install --save funex

Installation with Bower

bower install funex


// Declare a context with the allowed data
context = {
    dogs : {
        names: ["fido", "ricky"],
    join: function (a, b) { return a+"-"+b }

// Compile the expression into a function
fn = funex("join(dogs.names[0],[1])");

// Call the function with a context
var value = fn(context);

Usage with closures

// Declare the context with an array of objects with item 0 being the top most frame
context = [
        dogs : {
            names: ["fido", "ricky"],
        join: function (a, b) { return a+"-"+b }

// Compile the expression into a function
fn = funex("join(dogs.names[0],[1])");

// Call the function with a context
var value = fn(context);


Released in the Public Domain -



  • Apply unit tests to the minified build
  • Working support of all modern browsers
  • Document : Whitespace support
  • Document : Support for Multi-statement
  • Document : Code Quality and Hygiene
  • Document : Support for inline JSON (No litterals)
  • Document : Available Dists
  • Document: Lower cyclomatic complexity : all functions under 5
  • A new logo


  • A pretty homepage
  • provide a base memory frame when creating the funex
  • primitives like true, false, this


  • Benchmarks
  • Automate test suite on the frontend in all browsers (testling or sauce labs)
  • Syntax error on unclosed function calls and array gets
  • Syntax error on miss-placed string test."string"
  • Syntax error on unterminated statement


  • A api to tap property access and function calls
  • A tool to try/test funex live
  • Better sample usage
  • 100% Annotated code
  • Support evaluation of async expressions with a standard callback


  • Capacity setting: multi-statement ()
  • Capacity setting: JSON
  • Capacity setting: true/false primitives (true)
  • Capacity setting: validator for function calls
  • Capacity setting: validator for property access
  • Capacity setting: validator for value access
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