A JSON view engine for express

Usage no npm install needed!

<script type="module">
  import expressJsonViews from '';



A JSON view engine for the express framework to render objects and arrays with views written in JSON and helper functions.

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Even though express can send JSON responses out of the box by just retuning, in a lot of cases the response object or database models needs to be formatted. Think like DTOs in Java. Unnecessary or sensitive information like passwords need to be omitted, values need to be formatted and sub-objects/lists need to be altered as well.


  • Recursively render objects and arrays
  • Omit values
  • Rename object keys
  • Format values using helpers
  • Sub views and lists
  • View caching


$ npm install express-json-views
$ yarn add express-json-views
var app = require('express')();
var viewEngine = require('express-json-views');

app.engine('json', viewEngine({
       helpers: require('./views/helpers')
app.set('views', __dirname + '/views');
app.set('view engine', 'json');

Features & examples

Defining views

Views are defined using JSON files and located in a single directory in your project.

    "id": {},
    "slug": {
        "format": "getPostSlug"
    "title": {},
    "content": {
        "from": "content_text"
    "author": {
        "view": "user"
    "comments": {
        "view": "comment"
    "published_date": {}

The keys of the view are the keys which will be rendered into to resulting object. The default configuration {} just copies the value from the passed data. Possible configurations are:

  • from: Uses this value to lookup the value in the data object instead of the view key.
  • format: Calls a helper function with this name. Passes the value and the full object as arguments.
  • view: Defines the view if this value should be rendered with a different view. Value must be an Array or objects or an Object.

Rendering objects and lists

You don't have to worry about whether you want to render a single object or a list of objects. The view engine detects if you pass an array and will iterate over it. call res.render(...) and pass the view name and an object with a property called data which contains your data.

app.get('/posts', function (req, res) {

    var posts; // Query from database

    res.render('post', {
        data: posts



To define helpers you pass an object of functions when creating the view engine.

var helpers = {
    date: function (value, object) {
        if (!value) {
            return null;
        return dateFormat(value, 'yyyy-mm-dd');

app.engine('json', viewEngine({ helpers: helpers }));

Helper functions get 2 arguments, value and the full object. To calculate a value based on other values in the object you can use the second argument.

var helpers = {
    comment_count: function (value, object) {
        // Value will be null since this is a dynamic property and not present in the data object
        return object.comments ? object.comments.length : 0;

If you return a Promise the view engine will resolve use it. Though I would strongly advise you, not to do async calls here.


$ npm test