This parser accepts JsonLogic rules and executes them in JavaScript.
The JsonLogic format is designed to allow you to share rules (logic) between front-end and back-end code (regardless of language difference), even to store logic along with a record in a database. JsonLogic is documented extensively at JsonLogic.com, including examples of every supported operation and a place to try out rules in your browser.
The same format can also be executed in PHP by the library json-logic-php
jsonLogic.apply( { "==" : [1, 1] } );
// true
This is a simple test, equivalent to 1 == 1
. A few things about the format:
- The operator is always in the "key" position. There is only one key per JsonLogic rule.
- The values are typically an array.
- Each value can be a string, number, boolean, array (non-associative), or null
Here we're beginning to nest rules.
jsonLogic.apply(
{"and" : [
{ ">" : [3,1] },
{ "<" : [1,3] }
] }
);
// true
In an infix language (like JavaScript) this could be written as:
( (3 > 1) && (1 < 3) )
Obviously these rules aren't very interesting if they can only take static literal data. Typically jsonLogic
will be called with a rule object and a data object. You can use the var
operator to get attributes of the data object:
jsonLogic.apply(
{ "var" : ["a"] }, // Rule
{ a : 1, b : 2 } // Data
);
// 1
If you like, we support syntactic sugar on unary operators to skip the array around values:
jsonLogic.apply(
{ "var" : "a" },
{ a : 1, b : 2 }
);
// 1
You can also use the var
operator to access an array by numeric index:
jsonLogic.apply(
{"var" : 1 },
[ "apple", "banana", "carrot" ]
);
// "banana"
Here's a complex rule that mixes literals and data. The pie isn't ready to eat unless it's cooler than 110 degrees, and filled with apples.
var rules = { "and" : [
{"<" : [ { "var" : "temp" }, 110 ]},
{"==" : [ { "var" : "pie.filling" }, "apple" ] }
] };
var data = { "temp" : 100, "pie" : { "filling" : "apple" } };
jsonLogic.apply(rules, data);
// true
Sometimes the rule you want to process is "Always" or "Never." If the first parameter passed to jsonLogic
is a non-object, non-associative-array, it is returned immediately.
//Always
jsonLogic.apply(true, data_will_be_ignored);
// true
//Never
jsonLogic.apply(false, i_wasnt_even_supposed_to_be_here);
// false
To parse JsonLogic rules in a JavaScript frontend, install this library is via Bower:
bower install --save json-logic-js
To parse JsonLogic rules in a JavaScript backend (like Node.js), install this library via NPM:
npm install json-logic-js
Note that this project uses a module loader that also makes it suitable for RequireJS projects.
If that doesn't suit you, and you want to manage updates yourself, the entire library is self-contained in logic.js
and you can download it straight into your project as you see fit.
curl -O https://raw.githubusercontent.com/jwadhams/json-logic-js/master/logic.js
This library makes use of Array.map
and Array.reduce
, so it's not exactly Internet Explorer 8 friendly.
If you want to use JsonLogic and support deprecated browsers, you could easily use BabelJS's polyfill or directly incorporate the polyfills documented on MDN for map and reduce.