jsep

What is jsep?

JSEP (JavaScript Expression Parser) is a lightweight JavaScript library that parses JavaScript expressions into an abstract syntax tree (AST). It is useful for evaluating expressions, building interpreters, or creating domain-specific languages.

What are jsep's main functionalities?

Parsing Expressions

JSEP can parse a string expression into an abstract syntax tree (AST). This is useful for analyzing or transforming expressions.

const jsep = require('jsep');
const ast = jsep('a + b * (c - d)');
console.log(JSON.stringify(ast, null, 2));

Custom Operators

JSEP allows you to add custom operators to the parser. This is useful for extending the language to support new operations.

const jsep = require('jsep');
jsep.addBinaryOp('**', 10);
const ast = jsep('a ** b');
console.log(JSON.stringify(ast, null, 2));

Custom Functions

JSEP allows you to add custom functions to the parser. This is useful for extending the language to support new functions.

const jsep = require('jsep');
jsep.addUnaryOp('sqrt');
const ast = jsep('sqrt(a)');
console.log(JSON.stringify(ast, null, 2));

Other packages similar to jsep

mathjs

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser that can evaluate mathematical expressions. Compared to JSEP, Math.js offers a broader range of mathematical functions and utilities, but it is also larger in size.

expr-eval

Expr-eval is a small, fast JavaScript expression parser and evaluator. It supports basic arithmetic, logical operations, and custom functions. Compared to JSEP, expr-eval includes built-in evaluation capabilities, making it more suitable for direct expression evaluation.

jison

Jison is a parser generator that converts a grammar specification into a JavaScript parser. It is more powerful and flexible than JSEP, allowing for the creation of complex parsers for custom languages. However, it requires more setup and configuration.

README

jsep: A Tiny JavaScript Expression Parser

jsep is a simple expression parser written in JavaScript. It can parse JavaScript expressions but not operations. The difference between expressions and operations is akin to the difference between a cell in an Excel spreadsheet vs. a proper JavaScript program.

Why jsep?

I wanted a lightweight, tiny parser to be included in one of my other libraries. esprima and other parsers are great, but had more power than I need and were way too large to be included in a library that I wanted to keep relatively small.

jsep's output is almost identical to esprima's, which is in turn based on SpiderMonkey's.

Custom Build

First, install Grunt. While in the jsep project directory, run:

npm install .
grunt

The jsep built files will be in the build/ directory.

Usage

Client-side

<script src="/PATH/TO/jsep.min.js" type="text/javascript"></script>
...
var parse_tree = jsep("1 + 1");

Node.JS

First, run npm install jsep. Then, in your source file:

var jsep = require("jsep");
var parse_tree = jsep("1 + 1");

Custom Operators

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

// Add a custom @ unary operator with precedence 10
jsep.addUnaryOp('@');

// Remove a binary operator
jsep.removeBinaryOp(">>>");

// Remove a unary operator
jsep.removeUnaryOp("~");

License

jsep is under the MIT license. See LICENSE file.

Thanks

Some parts of the latest version of jsep were adapted from the esprima parser.

Changelog

0.3.2 - 2017-08-31

Notice

First version that was using a CHANGELOG.md.

Added

• Typings
• Functions to remove all binary/unary/etc. ops.

Fixed

• Supports multiline expressions.