React force update to the whole component tree

Sometimes in order to improve performance, you might consider using this.forceUpdate() within a react component.
this will force an update to the whole tree below this component to render, without checking if there were actually any changes.

use it with caution, and only when you are sure that the whole tree should re-render. for instance when you have a large table, and you allow a user to change which columns are visible. you know for sure that all rows should re-render, so you can help React, by telling it to skip the dirty checking, and simply re-render the whole thing. it drastically improves performance in this case.

Mocking AJAX responses by using a Media type string

When you want to test how your code handles API requests, or any AJAX requests – you will most likely find yourself in a situation where you don’t actually test the code responsible for the request, but just a “hardcoded” response that you provide in the code.

it might look like that:

if (testEnv) {
        foo: 'bar'
} else {
    $.get('/api/get_response_url').success(function(res) {

in most cases it will do just fine – but what if there is a complex and crucial functionality within the .success callback?

the answer would be: Mock AJAX response while preserving the actual request code block. like this:

var url = '/api/get_response_url';

if (testEnv) {
    url = 'data:application/json,{"foo":"bar"}';

$.get(url).success(function(res) {

in the above example we are setting the request url to be a media type string, which consists of:

  • top level type: data
  • type: application
  • subtype: json
  • parameters: {“foo”: “bar”}

you can read more about media types and their syntax here.

The request we do now returns what it has in the media type parameter – which is a completely valid, actual AJAX request with our mock response.

Maintain cursor position after changing an input value programatically

Sometimes you want to programatically change an input value, like in a case of input validation.
replacing an input value is easy, but has a common drawback – the cursor position will reset.

to overcome it, we can use this simple JS snippet:

function handleInputValueChange(e) {

    var cursorStart =,
        cursorEnd =;

        // value manipulations..., cursorEnd);

* note that this specific snippet relies on passing an event, onChange for instance.

setState not being updated on time

Say you have two functions in your React app that call setState(), and are dependant one on the other. you might stumble upon a case where the second function excepts to have the new state – but doesn’t.

That happens because setState() doesn’t immediately mutate the state (this.state) but creates a pending state transition. therefore, accessing this.state might return the existing value.

to overcome this, this.setState supports a callback function to be triggered once it’s been updated.

this.setState(newStateObj, () => {});

React, Redux and WebPack environment config

A brief description of the project at hand:

The task is to move existing sections that were built on top of RoR, with assets served with the rails asset pipeline. the files should be completely independent, loaded in a smart & efficient way.

The stack we decided to use was React with Redux, and Webpack as our build tool.

Folder & file structure

At first we started working with the standard redux structure, that goes like this:


It felt like a good start, because everything, literally – was in one place. all reducers, all actions, all components – in one place. it was quite easy to kick start and dive into work.

but, as the application grew, and more components were added, we reached to a point where the navigation in the code became complex and time consuming.
at this point we decided to look for a better solution.

The best solution we found for our needs was to use what’s called a folder by domain/feature structure, which looks like this:


Inspired by this lovely article.

It allows us to better consolidate components, and their respective actions, reducers and constants. basically a complete separation of mostly independent components.

Another perk by using this approach – the navigation in your IDE became much easier, and you don’t have to rely on seeing in which directory your file is located.

Building the webpack.config file(s).

  1. entry & output
    Because we need to work on multiple sections that will be built with react, and we don’t want to configure same settings over and over, we want webpack to output a dependencies file, and section file(s).

dependencies file – will hold any cross section relevant dependancies, like react, react-dom, react-router, isomorphic-fetch, etc.
section file(s) – each file will be name as react-<section>.js and will hold only it’s section relevant code.

entry: {
    killer_feature: './src/killer-feature/router',
    dependencies: [
output: {
    path: './build/',
    filename: "react-[name].js.erb"

The snippet above contains these entry points:
“killer_feature” – a section file entry point, in our case it’s the router config file that handles the killer_feature’s routes
“dependencies” – a list of all global modules that will be used by all other sections, like our killer_feature

and the output will be:

* note the .js.erb suffix – it’s ruby on rails file, that outputs as an ordinary .js file


2. externals configuration

externals are modules that we don’t want to include in our webpack build, but we do want it to be accessible from within our modules.
in my case I need lodash to be external, as it’s already being loaded in the rails app (not covered here)

externals: {
    'lodash': '_'

the ‘_’ is the object name by whom it will be referenced.

3. WebPack plugins

List of plugins that are used to optimize webpack’s output.

plugins: [
     new webpack.ProvidePlugin({
         React: 'react',
         ReactDOM: 'react-dom',
         ReactRouter: 'react-router',
         ReactRedux: 'react-redux',
         Redux: 'redux',
         ReduxThunk: 'redux-thunk',
         Immutable: 'immutable',
         fetch: 'isomorphic-fetch',
         Autocomplete: 'react-autocomplete'
     new webpack.DefinePlugin({
         'process.env': {
             'NODE_ENV': JSON.stringify('production')
     new webpack.optimize.OccurrenceOrderPlugin(),
     new webpack.optimize.DedupePlugin(),
     new webpack.optimize.CommonsChunkPlugin({
         name: 'dependencies',
         minChunks: Infinity
     new webpack.optimize.UglifyJsPlugin({
         test: /\.js\.erb/i,
         output: {
             quote_style: 3 
         compressor: {
             warnings: false

a few words about the used plugins:

ProvidePlugin – allows us to provide the modules in the list as plugins, available globally in any file, instead of requiring them every time at the top of each file. we do that for our dependancies files. (not recommended to use for non globally used files).
DefinePlugin – defines a global variable, that holds our NODE_ENV var. to be used to separate production/dev/test builds for instance.

OccurrenceOrderPlugin –  Assign the module and chunk ids by occurrence count. Ids that are used often get lower (shorter) ids. This make ids predictable, reduces to total file size and is recommended.

DedupePlugin – Search for equal or similar files and deduplicate them in the output.
CommonsChunkPlugin – Allows webpack to determine commonly used chunks of code, and pull them into a single separate file.

UglifyJsPlugin – Minifies & uglifies the output, reduces the output size drastically.

for further reference, check this doc:

Script control attributes

As part of the HTML5 spec, there are two attributes that allow control over when and how JS scripts are executed:

Default script control

<script src="plugins.js"></script>

When no script control presents – The script is downloaded and executed immediately, before the browser continues parsing the page.

Defer script control

<script src="plugins.js" defer></script>

Adding the defer attribute tells the browser to wait with executing the script until it finishes processing the document. commonly used when the script to be loaded is reliant on the DOM structure.

Async script control

<script src="social-plugins.js" async></script>

Adding the async attribute tells the browser that the script can be safely executed asynchronously. that’s good in cases where the script can act as a stand-alone script which does not rely on the DOM being ready first.

A visual example

script-controls visualization

JavaScript loading times

What is a JavaScript loading time?

JavaScript loading time is a point in time of the loading & execution of the page in where another JS script could be injected.

There are multiple loading times, and each of them should be used wisely, in order to achieve the fastest loading times of your app.

The main JavaScript loading times are:

  • Scripts loaded within the <head> tag
  • Scripts loaded at the bottom of the <body> tag
  • Scripts loaded after window.onload event
  • Scripts loaded on demand

Loading scripts within the <head> tag

Script files loaded in the <head> prevent the document body from rendering, which results in a blank page being displayed to the user while the browser waits to download and execute the script.

This is commonly known as JavaScript blocking.

As such, most web applications will only load script files in the <head> if it’s absolutely necessary for the script to do its job – for instance, analytics software that tracks user behaviour needs to be loaded as early as possible in order to accurately track everything.

Loading scripts at the bottom of the <body> tag

Loading your JS files at the bottom of the <body>, right after the content, allows the page to render completely before starting to download and execute javascript. by rendering I mean loading all of the html & images.

This loading method is considered as one of the best practices in JS loading times. In this area you should include all of the scripts that are necessary to be on the page at the page load – for example JS libraries like jQuery.

The most important thing to remember about this loading time – make sure you load the bare minimum required code for functionality. any other code should be loaded on demand.

Loading scripts after window.onload event

The load event – is triggered after the HTML & JS within the <body> has finished loading & executing.

At this point the browser is no longer “busy”, and it would be a good time to load non core functionality code.
for example – chat widget, feedback form, etc…

In order to load scripts on demand you should use a simple loading tool like RequireJS.

Loading scripts on demand

Loading on demand can happen at any point in time, based on how the user is interacting with the application. it will be done the same way as loading scripts on the window.load event, using a script loader.

This method is very useful when certain functionality is not needed when you load the page, but only on certain cases. For example: only when a user focuses on the search input, we will load the autocomplete functionality.