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    1.0.14 • Public • Published


    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:

    1. The operator is always in the "key" position. There is only one key per JsonLogic rule.
    2. The values are typically an array.
    3. Each value can be a string, number, boolean, array (non-associative), or null


    Here we're beginning to nest rules.

      {"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:

      { "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:

      { "var" : "a" },
      { a : 1, b : 2 }
    // 1

    You can also use the var operator to access an array by numeric index:

      {"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

    Always and Never

    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.

    jsonLogic.apply(true, data_will_be_ignored);
    // true
    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.


    npm i @jeremywall/json-logic-js

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