a tiny JavaScript expression parser

Download v0.4.0 1kb minified & gzipped

jsep is a JavaScript parser for JavaScript expressions. jsep is able to parse expressions like x * (1 + 2) or foo(bar.baz[0]) and convert them into an AST. jsep works in both server-side and client-side JavaScript.

jsep does not parse JavaScript operations (e.g. var a = b;) nor blocks of code (e.g. if (...) {...}.) Think of jsep as a tool to parse the kinds of expressions that would be written in individual Excel cells.

jsep was originally written as part of ConstraintJS and was extracted as a useful module for cases where full parsers like Esprima are too heavyweight.

The easiest way to use jsep is to use the download link above. To build the latest version from code, you'll first need node.js, npm, git. Then, run the following command in your terminal:
git clone https://github.com/EricSmekens/jsep.git
cd jsep
npm install
npm run build
The output will be in the dist/ directory.

Including jsep:


The simplest way to use jsep is to import it in your JS code:

import jsep from "PATH/TO/dist/jsep.min.js";

// Use jsep:
jsep("1 + 1");

Please note that for this to work, your the <script> element with your code needs to have type="module"

Note that you don't need to name the import jsep, you can name it anything you want. E.g. this works just as well:

import parse from "PATH/TO/dist/jsep.min.js";

// Use jsep:
parse("1 + 1");

If you want to use jsep as a global (legacy style):

<script src="PATH/TO/dist/jsep.iife.min.js"></script>
// After running npm install jsep
let jsep = require("jsep");


let parse_tree = jsep("1 + 1");

Custom Operators:

jsep also allows user-defined operators to be created.

// Add a custom ^ binary operator with precedence 10
jsep.addBinaryOp("^", 10);

// Add a custom @ unary operator with precedence 10

// Remove a binary operator

// Remove a unary operator