Expr2fn NPM | npm.io

expr2fn

A JavaScript library allows you to dynamically execute JavaScript expressions with speed and safety.

Quickstart

Install:
```
npm install expr2fn
```

Add to your project:

// File: app.ts
import expr2fn from 'expr2fn';

// Create an expression
const expr = 'a.b[0] + c() - d["e"]';

// Compile the expression
const fn = expr2fn(expr);

// Execute the compiled function within a context
const ctx = {
  a: {
    b: [1, 2, 3]
  },
  c: () => 4,
  d: {
    e: 5
  }
};
const val = fn(ctx); // => 0

// You can also execute an expression without providing a context
expr2fn('12')(); // => 12

Installation

Follow the steps below to get started with this project's development environment:

Install Node (v13.x+).

Clone this repository and navidate into it:

git clone https://github.com/paveew/expr2fn.git
cd expr2fn

Install the dependencies:
```
npm install
```
Test:
```
npm run test
```

You are ready to develop!

API

expr2fn()

Compile an expression into an executable function. The valid syntax for expressions is a subset of JavaScript syntax, as follows:

Literals
- Number
- String
- Boolean
- Object
- Array
- null and undefined
Operators:
- Unary: +, - and !
- Multiplicative: *, / and %
- Additive: + and -
- Relational: >, <, >= and <=
- Equality: ==, !=, === and !==
- Logical: && and ||
- Ternary: ? and :
Function/Method Call

The precedence of above operators is the same as in JavaScript. You can also use parentheses to change the precedence.

Why use `expr2fn`

The common way to dynamically execute JavaScript expressions is to use eval or Function. However, expr2fn has advantages in the following aspects:

Efficiency

When you use eval to evaluate a same expression multiple times, the expression is compiled by the JavaScript interpreter each time.

By using expr2fn, the same expression is compiled only once, no matter how many times the returned function is invoked, just like how Function works!