A simple, safe, JavaScript expression engine, allowing end-users to enter arbitrary boolean algebra expressions and converting them to an filter tree which can easily be used to query a data base or create beautiful visualizations as show below.
Built using JISON, a JavaScript parser generator based of on Flex and Bison
AI and impact and (ethics or ethical or Ai ethics or “artifical intelligence ethiscs”) and not (green ethics or WECAN)Sure, you could do that with vanilla JavaScript and eval(), but that is very unsafe as it can be used to launch cross-site scripting (XSS) attacks or SQL injection.
Filtrex defines a really simple expression language that should be familiar to anyone who's ever used a spreadsheet and compile it into a JavaScript function at runtime.
example of a filter tree
- Simple! Very easy to adapt to ur requirements
- Fast! Expressions get compiled into JavaScript functions, offering the same performance as if it had been hand coded. e.g.
- Safe! You as the developer have control of which data can be accessed and the functions that can be called. Expressions cannot escape the sandbox.
- Pluggable! Add your own data and functions.
- Predictable! Because users can't define loops or recursive functions, you know you won't be left hanging.
Under the hood, the above expression gets compiled to a clean and fast Filter Tree, looking something like this:
There are only 2 types: numbers and strings. Numbers may be floating point or integers. Boolean logic is applied on the truthy value of values (e.g. any non-zero number is true, any non-empty string is true, otherwise false).
| Values | Description |
|---|---|
| 43, -1.234 | Numbers |
| "hello" | String |
| foo, a.b.c, 'foo-bar' | External data variable defined by application (may be numbers or strings) |
| Numeric arithmetic | Description |
|---|---|
| x + y | Add |
| x - y | Subtract |
| x * y | Multiply |
| x / y | Divide |
| x % y | Modulo |
| x ^ y | Power |
| Comparisons | Description |
|---|---|
| x == y | Equals |
| x < y | Less than |
| x <= y | Less than or equal to |
| x > y | Greater than |
| x >= y | Greater than or equal to |
| x ~= y | Regular expression match |
| x in (a, b, c) | Equivalent to (x == a or x == b or x == c) |
| x not in (a, b, c) | Equivalent to (x != a and x != b and x != c) |
| Boolean logic | Description |
|---|---|
| x or y | Boolean or |
| x and y | Boolean and |
| not x | Boolean not |
| x ? y : z | If boolean x, value y, else z |
| ( x ) | Explicity operator precedence |
| Built-in functions | Description |
|---|---|
| abs(x) | Absolute value |
| ceil(x) | Round floating point up |
| floor(x) | Round floating point down |
| log(x) | Natural logarithm |
| max(a, b, c...) | Max value (variable length of args) |
| min(a, b, c...) | Min value (variable length of args) |
| random() | Random floating point from 0.0 to 1.0 |
| round(x) | Round floating point |
| sqrt(x) | Square root |
Operator precedence follows that of any sane language.
When integrating in to your application, you can add your own custom functions.
// Custom function: Return string length.
function strlen(s) {
return s.length;
}
// Compile expression to executable function
var myfilter = compileExpression(
'strlen(firstname) > 5',
{strlen:strlen}); // custom functions
myfilter({firstname:'Joe'}); // returns 0
myfilter({firstname:'Joseph'}); // returns 1Why the name?
Because it was originally built for FILTeR EXpressions.
What's Jison?
Jison is bundled with Filtrex – it's a JavaScript parser generator that does the underlying hard work of understanding the expression. It's based on Flex and Bison.
What happens if the expression is malformed?
Calling compileExpression() with a malformed expression will throw an exception. You can catch that and display feedback to the user. A good UI pattern is to attempt to compile on each keystroke and continuously indicate whether the expression is valid.