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    JavaScript implementation of the JSONata query and transformation language.


    • npm install jsonata


    In Node.js:

    var jsonata = require("jsonata");
    var data = {
      example: [
        {value: 4},
        {value: 7},
        {value: 13}
    var expression = jsonata("$sum(example.value)");
    var result = expression.evaluate(data);  // returns 24

    In a browser:

    <!DOCTYPE html>
    <html lang="en">
        <meta charset="UTF-8">
        <title>JSONata test</title>
        <script src="lib/jsonata.js"></script> 
          function greeting() {
            var json = JSON.parse(document.getElementById('json').value);
            var result = jsonata('"Hello, " & name').evaluate(json);
            document.getElementById('greeting').innerHTML = result;
        <textarea id="json">{ "name": "Wilbur" }</textarea>
        <button onclick="greeting()">Click me</button>
        <p id="greeting"></p>

    jsonata uses ES2015 features such as generators. For browsers lacking these features, lib/jsonata-es5.js is provided.



    Parse a string str as a JSONata expression and return a compiled JSONata expression object.

    var expression = jsonata("$sum(example.value)");

    If the expression is not valid JSONata, an Error is thrown containing information about the nature of the syntax error, for example:

      code: "S0202",
      stack: "...",
      position: 16,
      token: "}",
      value: "]",
      message: "Syntax error: expected ']' got '}'"

    expression has three methods:

    expression.evaluate(input[, bindings[, callback]])

    Run the compiled JSONata expression against object input and return the result as a new object.

    var result = expression.evaluate({example: [{value: 4}, {value: 7}, {value: 13}]});

    input should be a JavaScript value such as would be returned from JSON.parse(). If input could not have been parsed from a JSON string (is circular, contains functions, ...), evaluate's behaviour is not defined. result is a new JavaScript value suitable for JSON.stringify()ing.

    bindings, if present, contains variable names and values (including functions) to be bound:

    jsonata("$a + $b()").evaluate({}, {a: 4, b: () => 78});
    // returns 82

    expression.evaluate() may throw a run-time Error:

    var expression = jsonata("$notafunction()"); // OK, valid JSONata
    expression.evaluate({}); // Throws

    The Error contains information about the nature of the run-time error, for example:

      code: "T1006",
      stack: "...",
      position: 14,
      token: "notafunction",
      message: "Attempted to invoke a non-function"

    If callback(err, value) is supplied, expression.evaluate() returns undefined, the expression is run asynchronously and the Error or result is passed to callback.

    jsonata("7 + 12").evaluate({}, {}, (error, result) => {
      if(error) {
      console.log("Finished with", result);
    // Prints "Started", then "Finished with 19"

    expression.assign(name, value)

    Permanently binds a value to a name in the expression, similar to how bindings worked above. Modifies expression in place and returns undefined. Useful in a JSONata expression factory.

    var expression = jsonata("$a + $b()");
    expression.assign("a", 4);
    expression.assign("b", () => 1);
    expression.evaluate({}); // 5

    Note that the bindings argument in the expression.evaluate() call clobbers these values:

    expression.evaluate({}, {a: 109}); // 110

    expression.registerFunction(name, implementation[, signature])

    Permanently binds a function to a name in the expression.

    var expression = jsonata("$greet()");
    expression.registerFunction("greet", () => "Hello world");
    expression.evaluate({}); // "Hello world"

    You can do this using expression.assign or bindings in expression.evaluate, but expression.registerFunction allows you to specify a function signature. This is a terse string which tells JSONata the expected input argument types and return value type of the function. JSONata raises a run-time error if the actual input argument types do not match (the return value type is not checked yet).

    var expression = jsonata("$add(61, 10005)");
    expression.registerFunction("add", (a, b) => a + b, "<nn:n>");
    expression.evaluate({}); // 10066

    Function signatures are specified like so:

    Function signature syntax

    A function signature is a string of the form <params:return>. params is a sequence of type symbols, each one representing an input argument's type. return is a single type symbol representing the return value type.

    Type symbols work as follows:

    Simple types:

    • b - Boolean
    • n - number
    • s - string
    • l - null

    Complex types:

    • a - array
    • o - object
    • f - function

    Union types:

    • (sao) - string, array or object
    • (o) - same as o
    • u - equivalent to (bnsl) i.e. Boolean, number, string or null
    • j - any JSON type. Equivalent to (bnsloa) i.e. Boolean, number, string, null, object or array, but not function
    • x - any type. Equivalent to (bnsloaf)

    Parametrised types:

    • a<s> - array of strings
    • a<x> - array of values of any type

    Some examples of signatures of built-in JSONata functions:

    • $count has signature <a:n>; it accepts an array and returns a number.
    • $append has signature <aa:a>; it accepts two arrays and returns an array.
    • $sum has signature <a<n>:n>; it accepts an array of numbers and returns a number.
    • $reduce has signature <fa<j>:j>; it accepts a reducer function f and an a<j> (array of JSON objects) and returns a JSON object.

    Each type symbol may also have options applied.

    • + - one or more arguments of this type
      • E.g. $zip has signature <a+>; it accepts one array, or two arrays, or three arrays, or...
    • ? - optional argument
      • E.g. $join has signature <a<s>s?:s>; it accepts an array of strings and an optional joiner string which defaults to the empty string. It returns a string.
    • - - if this argument is missing, use the context value ("focus").
      • E.g. $length has signature <s-:n>; it can be called as $length(OrderID) (one argument) but equivalently as OrderID.$length().

    More information


    See the for details of how to contribute to this repo.


    npm i jsonata

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