The cheesy object formatter
Latest commit 055a641 Feb 17, 2016 Christian Johansen Format sets


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The cheesy object formatter

Pretty formatting of arbitrary JavaScript values. Currently only supports ascii formatting, suitable for command-line utilities. Like JSON.stringify, it formats objects recursively, but unlike JSON.stringify, it can handle regular expressions, functions, circular objects and more.

formatio is a general-purpose library. It works in browsers (including old and rowdy ones, like IE6) and Node. It will define itself as an AMD module if you want it to (i.e. if there's a define function available).

Running tests

npm test

Or use Buster.JS manually:

node_modules/buster/bin/buster-test --help

formatio.ascii API

formatio.ascii can take any JavaScript object and format it nicely as plain text. It uses the helper functions described below to format different types of objects.


object can be any kind of object, including DOM elements.

Simple object

var formatio = require("formatio");

var object = { name: "Christian" };

// Outputs:
// { name: "Christian" }

Complex object

var formatio = require("formatio");

var developer = {
    name: "Christian",
    interests: ["Programming", "Guitar", "TV"],

    location: {
        language: "Norway",
        city: "Oslo",

        getLatLon: function getLatLon(callback) {
            // ...

        distanceTo: function distanceTo(location) {

    speak: function () {
        return "Oh hi!";


// Outputs:
// {
//   interests: ["Programming", "Guitar", "TV"],
//   location: {
//     city: "Oslo",
//     distanceTo: function distanceTo() {},
//     getLatLon: function getLatLon() {},
//     language: "Norway"
//   },
//   name: "Christian",
//   speak: function () {}
// }

Custom constructor

If the object to format is not a generic Object object, formatio displays the type of object (i.e. name of constructor). Set the excludeConstructors (see below) property to control what constructors to include in formatted output.

var formatio = require("formatio");

function Person(name) { = name; }

var dude = new Person("Dude");

// Outputs:
// [Person] { name: "Dude" }

DOM elements

DOM elements are formatted as abbreviated HTML source. 20 characters of innerHTML is included, and if the content is longer, it is truncated with "[...]". Future editions will add the possibility to format nested markup structures.

var p = document.createElement("p"); = "sample";
p.className = "notice";
p.setAttribute("data-custom", "42");
p.innerHTML = "Hey there, here's some text for ya there buddy";


// Outputs
// &lt;p id="sample" class="notice" data-custom="42"&gt;Hey there, here's so[...]&lt;/p&gt;</code></pre>


Formats a function like "function [name]() {}". The name is retrieved from formatio.functionName.


Formats an array as "[item1, item2, item3]" where each item is formatted with formatio.ascii. Circular references are represented in the resulting string as "[Circular]".


Formats all properties of the object with formatio.ascii. If the object can be fully represented in 80 characters, it's formatted in one line. Otherwise, it's nicely indented over as many lines as necessary. Circular references are represented by "[Circular]".

Objects created with custom constructors will be formatted as "[ConstructorName] { ... }". Set the excludeConstructors property to control what constructors are included in the output like this.


Formats a DOM element as HTML source. The tag name is represented in lower-case and all attributes and their values are included. The element's content is included, up to 20 characters. If the length exceeds 20 characters, it's truncated with a "[...]".


Guesses a function's name. If the function defines the displayName property (used by some debugging tools <>_) it is preferred. If it is not found, the name property is tried. If no name can be found this way, an attempt is made to find the function name by looking at the function's toString() representation.


Attempts to guess the name of the constructor that created the object. It does so by getting the name of object.constructor using functionName. If a name is found, excludeConstructors is consulted. If the constructor name matches any of these elements, an empty string is returned, otherwise the name is returned.

formatio.ascii properties


Whether or not to quote simple strings. When set to false, simple strings are not quoted. Strings in arrays and objects will still be quoted, but ascii("Some string") will not gain additional quotes.


This property allows to limit the number of printed array elements or object properties. When set to 0, all elements will be included in output, any number greater than zero will set the limit to that number.

excludeConstructors (["Object", /^.$/])

An array of strings and/or regular expressions naming constructors that should be stripped from the formatted output. The default value skips objects created by Object and constructors that have one character names (which are typically used in Object.create shims).

While you can set this property directly on formatio.ascii, it is recommended to create an instance of formatio.ascii and override the property on that object.

Strings represent constructor names that should not be represented in the formatted output. Regular expressions are tested against constructor names when formatting. If the expression is a match, the constructor name is not included in the formatted output.

function Person(name) { = name;

var person = new Person("Chris");

// Outputs
// [Person] { name: "Chris" }

var formatter = Object.create(formatio);
formatter.excludeConstructors = ["Object", /^.$/, "Person"];

// Outputs
// { name: "Chris" }

// Global overwrite, generally not recommended
formatio.excludeConstructors = ["Object", /^.$/, "Person"];

// Outputs
// { name: "Chris" }


1.1.2 (12.12.2014)