fexpr is a filter query language parser that generates easy to work with AST structure so that you can safely create SQL, Elasticsearch, etc. queries from user input. fexpr.js is a typescript/javascript port of fexpr.

Or in other words, transform the string "id > 1" into the struct [{&& {{identifier id} > {number 1}}}].

Supports parenthesis and various conditional expression operators (see Grammar).

This is a zero-dependency(<5KB) library that works in both node.js and browser environments.

Almost a line by line port of fexpr (BSD 3-Clause License) by Gani Georgiev, from golang to typescript with minor changes.

Try the fexpr.js playground to see how the parser works. Check the index.html file for the example source code.

Read the package documentation or the source code for API documentation.

Installation

npm install fexpr.js

or use a cdn link in browser

ESM Usage in javascript or typescript:

import { parse } from 'fexpr.js';

const result = parse('id=123 && status="active"');
// result: [{&& {{identifier id} = {number 123}}} {&& {{identifier status} = {text active}}}]

CommonJS Usage in node.js:

const { parse } = require('fexpr.js');

const result = parse('id=123 && status="active"');

UMD Usage in browser:

<script src="https://cdn.jsdelivr.net/npm/fexpr.js"></script>
<script>
    const result = fexpr.parse('id=123 && status="active"');
</script>

Note that each parsed expression statement contains a join/union operator (&& or ||) so that the result can be consumed on small chunks without having to rely on the group/nesting context.

See the package documentation for more details and examples.

fexpr grammar resembles the SQL WHERE expression syntax. It recognizes several token types (identifiers, numbers, quoted text, expression operators, whitespaces, etc.).

You could find all supported tokens in scanner.ts.

• = Equal operator (eg. a=b)
• != NOT Equal operator (eg. a!=b)
• > Greater than operator (eg. a>b)
• >= Greater than or equal operator (eg. a>=b)
• < Less than or equal operator (eg. a<b)
• <= Less than or equal operator (eg. a<=b)
• ~ Like/Contains operator (eg. a~b)
• !~ NOT Like/Contains operator (eg. a!~b)
• ?= Array/Any equal operator (eg. a?=b)
• ?!= Array/Any NOT Equal operator (eg. a?!=b)
• ?> Array/Any Greater than operator (eg. a?>b)
• ?>= Array/Any Greater than or equal operator (eg. a?>=b)
• ?< Array/Any Less than or equal operator (eg. a?<b)
• ?<= Array/Any Less than or equal operator (eg. a?<=b)
• ?~ Array/Any Like/Contains operator (eg. a?~b)
• ?!~ Array/Any NOT Like/Contains operator (eg. a?!~b)
• && AND join operator (eg. a=b && c=d)
• || OR join operator (eg. a=b || c=d)
• () Parenthesis (eg. (a=1 && b=2) || (a=3 && b=4))

Number tokens are any integer or decimal numbers.

Example: 123, 10.50, -14.

Identifier tokens are literals that start with a letter, _, @ or # and could contain further any number of letters, digits, . (usually used as a separator) or : (usually used as modifier) characters.

Example: id, a.b.c, field123, @request.method, author.name:length.

Text tokens are any literals that are wrapped by ' or " quotes.

Example: 'Lorem ipsum dolor 123!', "escaped \"word\"", "mixed 'quotes' are fine".

Comment tokens are any single line text literals starting with //. Similar to whitespaces, comments are ignored by fexpr.parse().

Example: // test.

The tokenizer (aka. fexpr.Scanner) could be used without the parser's state machine so that you can write your own custom tokens processing:

import { Scanner } from 'fexpr.js';

const s = new Scanner('id > 123');

// scan single token at a time until EOF or error is reached
while (true) {
    const t = s.scan();
    if (t.type === 'EOF' || t.error) {
        break;
    }

    console.log(t);
}

// Output:
// {type: 'identifier', value: 'id'}
// {type: 'whitespace', value: ' '}
// {type: 'sign', value: '>'}
// {type: 'whitespace', value: ' '}
// {type: 'number', value: '123'}