es-eval

Evaluate JavaScript expressions safely. No more being afraid of what the users enter!

🎲 Playground (pre-release version)

Installation

npm i es-eval

Usage

// Simple expression
const esEval = require('es-eval');

const result = esEval('1 + 2');
console.log(result); // Output: 3

// User values
const esEval = require('es-eval');

const result = esEval('1 + x', { x: 4 });
console.log(result); // Output: 5

Or more complex examples:

// IIFE example
const esEval = require('es-eval');

const exp = `(() => {
  const out = [];

  const callback = () => {
    out.push('callback() called');
  };

  const main = function (param, cb) {
    out.push('main() started with param = "' + param + '"');
    cb();
    out.push('main() finished');
  };

  main('My value', callback);

  return out;
})()`;

console.log(esEval(exp));
// Output: [
//   'main() called with My value',
//   'Callback called!',
//   'main() finished'
// ]

// Hangup protection in infinite loop
const esEval = require('es-eval');

try {
  esEval(`(() => {
    while (true) {}
  })()`);
} catch (err) {
  console.log(err.message); // Output: 'Evaluation timeout'
}

Features

Feature	Notes
Hangup protection	The execution of any user inputs is protected against intentional or unintentional hangups. Since it is mathematically proven that the halting problem is undecidable, hence it cannot be automatically computed, this protection is based on a configurable timeout.
Primitive values	number, string, boolean and undefined values.
Objects	{ key: 'value' }, null, built-in static methods: Object.entries(), Object.keys(), Object.values()
Arrays	[1, 2, 3], built-in properties and methods: length, push, pop, shift, ushift, slice, splice, forEach, map, filter, reduce, includes
Arrow function expressions	(x, y) => x + y
Standard function expressions	function () { return 'value'; }
Closures
Nested expressions	(a < (b + 1) && a - (a < ([1, 2].map(x => 1 + x)).length))
Callbacks	cb => { cb(); return 1; }
Mathematical operations	+, -, /, *, %, **
Comparators	===, !==, ==, !=, <, >, <=, >=
Logical operations	&&, ||, !
Bitwise operations	&, |, ^
Ternary operator	... ? ... : ...
Nullish operator	??
Variables	const and let declarations. Assignments.
Conditional	if...else statement.
Loops	while and for...of statements.
JSON	JSON.parse() and JSON.stringify().
Math	Math.random(), Math.min(), Math.max(), Math.floor(), Math.ceil() and Math.round().
Spread operator (...)	Spread syntax for arrays, objects, and parameters.
Global functions	parseFloat, parseInt, isNaN and isFinite.

Coming soon...

Status	Feature	Notes
😓 In Progress	global this	Reference to the global object.
😓 In Progress	Array.isArray()	Determines whether the passed value is an Array.
😓 In Progress	+= operator	Addition assignment.
⏳ To-Do	Array.from()	Creates a copy of an iterable or array-like object.
⏳ To-Do	Array.of()	Creates an array from the arguments.
⏳ To-Do	Block evaluation	Run a block code and return the block context variables with the values at the end of the execution.

Future features

📨 Vote what's coming on! 💡 or Suggest your ideas.

Feature	Notes
Browser support
for in loop
for (;;) loop
do ... while loop
Destructuring
And a lot more!...

How it works?

• It never executes user code passing it to JS engine (no eval(), no new Function(...), no vm, no other third party engines), making sure the evaluation is safe.
• No access to require/import modules.
• No access to OS features like file system, network, etc.
• No access to global objects.
• All user code is parsed to an AST and analyzed step by step, representing the code statements and functions in own components. No native functions are created with the user input.
• All access to global objects is emulated and there's no real access to natives.
• Standard ECMAScript features are implemented and not delegated to the underlying engine.

What is this for

✅ Evaluate user input expressions safely

✅ Easily provide a way to enter and evaluate custom conditions

✅ Embed JS expressions in template engines

✅ Parse custom JS functions once and evaluate them many times

✅ Create expressions with context values, including objects and arrays

What is this NOT for

⛔ Create entire applications

⛔ Replace V8, or other JS engines