Tag Archives: reactjs

Parsing Hash Args for Cognito Auth – Javascript

Hi everyone,

A quick post on a function for parsing hash args when using AWS Congito.

Just in case the fiddle ever disappears:

const parseHashArgs = aURL => {

  aURL = aURL || window.location.href;

  var vars = {};
  var hashes = aURL.slice(aURL.indexOf('#') + 1).split('&');

  for (var i = 0; i < hashes.length; i++) {
    var hash = hashes[i].split('=');

    if (hash.length > 1) {
      vars[hash[0]] = hash[1];
    } else {
      vars[hash[0]] = null;

  return vars;


Thanks to this link on Github: https://gist.github.com/miohtama/1570295/289d5a82e65663c9b515c88186a268c6dd1fddb7

NavLink ListItems not Applying activeClassName class when Clicked On – ReactJS React-Router MaterialUI

Hi everyone,

A bit of a hairy issue I ran into today that took a while to track down. I’m using React Router with Material UI to render a Drawer as a sidebar:

The issue was that some links were not applying the expected activeclass:

<ListItem button component={NavLink} to="/about" onClick={this.handleItemClick} className={classes.sidebarContentListItem} activeClassName={classes.active}>
	<ListItemIcon className={classes.sidebarText}>
		<Info />
	<ListItemText primary={
		<Typography type="body2" className={classes.sidebarText}>
	} />

After trawling through react-router I eventually found a post on github that mentioned a similar issue: https://github.com/ReactTraining/react-router/issues/4638

The solution turned out to be wrapping all relevant components with withrouter.

Uncaught SyntaxError: Unexpected token < - ReactJS Build

Hi everyone,

A ReactJS issue I ran into after running npm run build:

Uncaught SyntaxError: Unexpected token <

This one took a while to track down but it essentially boils down to the built index.html file referencing paths relatively:

Issue: index.html was referencing
"<script ... src="./static/js/main.e7b5bb28.js"></script></body></html".
Instead of:
"<script ... src="/static/js/main.e7b5bb28.js"></script></body></html".

This meant that anytime a page was accessed directly it attempted to load the static files from the wrong directory. To fix it, I had to update the homepage node in package.json

"version": "0.1.0",
  "homepage": "./",
  "private": true,
Instead use:
"version": "0.1.0",
  "homepage": "/",
  "private": true,

Hopefully that’s able to help someone else out, took a while to track down!

npm ERR! missing script: flow npm ERR! A complete log of this run can be found in: – ReactJS and Flow

Hi everyone,

I ran into the following error while trying to setup flow:

npm ERR! missing script: flow
npm ERR! A complete log of this run can be found in:

To fix this, just add “flow”: “flow” as a new entry under “scripts” in your package.json file.

See the following link for more info:

Including an Externally Hosted Script in ReactJs

Hi everyone,

Just a quick example of how to include an externally hosted js file in a reactjs app. In index.html add your script tag as you would in a normal app:

    <script src="https://js.prelive.promisepay.com/PromisePay.js " type="text/javascript"></script>

Then in the file you plan to use the library you can add a const and reference it normally:

const promisepay = window.promisepay;

Thanks to this link for the info: https://stackoverflow.com/a/44877953/522859

Allow Number and String for PropTypes – ReactJS

Hi everyone,

A quick post on how to allow a string or number when defining PropTypes:

static propTypes = {
        numberField: PropTypes.number.isRequired,
        stringField: PropTypes.number.isRequired,
        mixedField: PropTypes.oneOfType([PropTypes.string, PropTypes.number]).isRequired

Thanks to this stackoverflow post for the info: https://stackoverflow.com/a/41808543/522859

Overriding Button Styles and Hover Effects – Material UI

Hi everyone,

Just a quick post on how to override the background color and hover effects for buttons in material ui:

Define your class as follows:

const styles = theme => ({
    greenButton: {
        backgroundColor: green[500],
        color: '#FFF',
        '&:hover': {
            backgroundColor: green[400],
            color: '#FFF'

Then just reference it as you normally would:

const styles = theme => ({
const { classes } = this.props;
<Button size="small" className={classes.greenButton} variant="raised">
      <AddShoppingCartIcon />

Multiple Instances of Component Firing Incorrect onChange – ReactJS

Hi everyone,

I ran into a bit of an issue today while trying to render multiple instances of a component on a single page. Each component had a file input that was bound with an onChange event. When triggered the onChange function referenced the first component placed on the page no matter which instance was clicked.

The issue ended up being that the id of the input fields coincidentally overlapped. This meant that there were multiple instances of the field on the page with the same id value. Ensuring that each one was unique resolved the issue.

Took a fair while to narrow this one down so hopefully it’ll be able to help someone else!


Avoiding Wrapper Divs in ReactJs

Hi everyone,

Just a quick post on how you can avoid wrapper divs in ReactJs. It’s particularly useful when populating tables or creating parts of a larger component. Instead of the following:

return (

You can use fragments:

import React, { Fragment } from 'react'
return (

The fragment won’t polute the dom and mean that you don’t need to add any additional styling. Check out these links for more info:

Adding a Link to a Drawer – Material UI and ReactJS

Hi everyone,

I ran into a bit of an issue turning a menuitem into a link with Material UI and React-Router. The main problems being that underlines appeared and threw the spacing out.

To summarize, use the component attribute on the ListItem:

   <ListItem button component={Link} to="https://www.whatibroke.com">
        <ListItemText primary="WhatIBroke" />

The official docs cover it here: https://material-ui.com/api/list-item/

See the following stackoverflow post for more info: https://stackoverflow.com/a/50558139/522859