JavaScript tip: format console.log output

You can format the output of console.log() using CSS. Use %c in your console log string and then add an argument for the CSS.

Here’s a simple script that uses CSS formatting to make a formatted console logger:

const fl = {
  log: function (title, message, color) {
    console.log('%c%s:%c %s', 
      `color: ${color}; font-weight: bold; text-decoration: underline ${color}`,
      'color: black',
      title, message);

  info: function (message) {
    this.log('Info', message, 'green');

  warning: function (message) {
    this.log('Warning', message, 'orange');

  error: function (message) {
    this.log('Error', message, 'red');


Here is the result in the console:

console formatting

Bug reproduction steps

To properly fix a bug, you must be able to reproduce it. If the developers can’t reproduce it they can only guess at its cause and their corrections are just potential fixes that can’t be validated.

If someone writes a report for a bug they can’t reproduce, how can they validate that the developer assigned to the task has satisfactorily fixed the problem? They can’t. So why report and track something that can’t be closed except by a leap of faith?

Maybe because the developer will find the reproduction steps? They might, but then again who stands a better chance of doing this?

The best person to reproduce a bug is the person who first encountered it. To give an analogy, it’s like if you found a secret glade in a forest and you can’t find it again. So you ask someone who’s never been there to find it for you and you don’t give them any directions. Even if they find one on their own, is it the same one you found?

Another situation is the QA or reporter can reproduce it, but the developer can’t. This might be because the reproduction steps aren’t clear or just missing. It could also be that there is a difference between the environments or actions of the reporter and the developer.

Sometimes the bug reporter has produced the issue but hasn’t tried to reproduce it consistently. They write down with they did but haven’t tested their steps further to see if they reproduce the original results every time.

All of these situations can be greatly mitigated by writing good reproduction steps and testing them before submitting the bug report.

How to write reproduction steps:

  • Most bugs report should include reproduction steps. If reproduction can’t be achieved, in most cases, testing should continue.
  • Steps should be clear and concise.
  • Each step should be absolutely necessary to reproduce the bug. This removes clutter but also forces the reporter to distill the bug to it’s most minimal conditions, which helps to define it correctly.
  • No assumptions should be made while writing the steps. This can be very hard as we all have implicit assumptions that are not apparent at first glance. For example, if a user was created for testing purposes, how was it created? What sort of user is it? Is the username included in the report?
  • Before submitting the report, the reproduction steps themselves should be tested. Did they reproduce the issue? Were some required operations omitted because the seemed evident? For example if navigation to a screen occurred and there are several ways to navigate to this screen, which one was used?
  • During the testing of the reproduction steps the scenario should be altered a little. Does the scenario still reproduce the bug with the alterations. If so the altered steps are either unnecessary or could be generalized further. Examples of this could be testing with a different user or changing the sequence of some operations.

In addition to the reproduction steps bug reports for mobile applications should include the OS and device name.

Bug reports for web applications should include the browser and it’s version in the case of Internet Explorer or non evergreen browsers.

All bug reports should include the version number of the application that was under test as well as the environment the bug was found on: dev, qa, prod.

Taking these steps will minimize the back and forth between QA and development and will reduce the time required to close bugs.


Preventing multiple calls on button in Angular

If you wish to prevent your users from clicking on a button multiple times in a row, for example if the button triggers some animation that needs to complete before being triggered again, you can use debouncing.

Debouncing is a form of rate limiting in which a function isn’t called until it hasn’t been called again for a certain amount of time. That is to say, if the debouncing time is 200ms, as long as you keep calling the function and those calls are within a 200ms window of each other, the function won’t get called.

You could use a button’s [disabled] attribute and setTimeout, but I have ran in some cases where this interfered with the ongoing animation of the first call.

Here is how to use RxJs with Angular to implement debouncing.

In your template just bind a function to an event like you would normally:


In your component use the following code:

import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
import 'rxjs/add/operator/debounceTime';

// ...
// ...
export class SomeComponent {
    private buttonClicked = new Subject();

    constructor() {
        const btnClickedObs = this.nextClicked
        btnClickedObs.subscribe(() => 

    doStuff() {;

Debouncing is similar to throttling. With throttling you limit the number of calls to 1 per time frame of unit so the first call happens automatically. If the user keeps mashing the button continuously, throttled calls will be made at a rate of 1 per throttleTime whereas with debouncing only one call will be made. Which one you want depends on your particular scenario.

You can mix both, but you must apply the debouncing before the throttling and the throttlingTime must be at least twice the debouncingTime. Otherwise one of them will have no effect.