README.md

js-safe-expression

A lightweight, CSP-safe and fast javascript expression parser/executor. The main usage for this project is to execute javascript code without using eval or Function. It is built on the top of the AngularJS 1 internal lexer/parser. It compiles & executes javascript strings using a provided scope such as "1+1" or "context.call_a_function()", "value = 'foo", "value === 'foo'"

This project can run on websites having a strict CSP policy and can be easily plugged on the top on frameworks such as Petite-Vue, AlpineJS, Preact.

The code is 19KB when minified and 5KB once gzipped

How to use?

Import the module in your code:

var SafeExpression = require("safe-expression");

var SafeExpression = require("safe-expression");

var execute = new SafeExpression();

// Returns 2
console.log(execute("1+1")());

// Returns 4
console.log(execute("1 + value")({
  value: 3
}));

// Returns true
console.log(execute("value === true")({
  value: 3
}));

// Executes a function
var store = {
  internal_code: () => {
    console.log("Executed") 
  }
};
execute("internal_code()")(store);

Caveats

• It is not currently supporting ++ and -- operators, so use test = test + 1 instead of test++
• Operands are not possible in function calls. For instance, context.call_a_function(index + 1) will execute context.call_a_function(index)

Notes about the autorship

This code is made from an extract of AngularJS's parser.

The main different with the original code is we changed all AngularJS internals so it can run as a standalone library, without embedding the rest of AngularJS.

Some AngularJS specific features got removed such as filters and watchers so it can work with a VanillaJS syntac