1) Using outdated HTML markup and tags.
Some markup elements are now considered obsolete. What was used in the 20th century is no longer relevant. For example, elements such as <table> for layout or <span> and <div> will look out of place in the new HTML standards, or even not be supported in recent browsers.
How to avoid this mistake:
Stop using elements that are inappropriate today. You can get acquainted with modern markup options on the corresponding sites, for example, on whatwg.org.
2) "This works in my browser, so it will work everywhere!".
This error seems so simple and straightforward, but it still needs to be announced. It often happens that you get used to and love one particular browser. Accordingly, you will test everything exclusively in it, forgetting that in other browsers, web pages may be displayed incorrectly.
How to avoid this mistake:
just regularly test your web pages in different browsers and their versions. There are now many good and free tools out there to help you check how your site will look in different browsers and their versions. Regularly checking the correctness of the display of your web page will make your level as a webmaster higher.
3) Too much work.
You are absorbed in a new project, deadlines are burning, and you did not notice how you worked for more than 10 hours. Sound familiar? Then it's your fault. Spending a lot of time on repetitive tasks or just writing codes for a long time, you not only get tired a lot but also make a lot of mistakes.
How to avoid this mistake:
You should explore possible options for automating simple actions. Programs such as Sublime Text or Visual Studio today offer many new techniques that make your daily work easier. Spend a little time exploring the advanced and additional new features and make your work easier.
4) Bulky codes
This error stems from the 2 errors mentioned above. You want your web page to display correctly in all browsers, and because of this, you create code that will respond to any scenario. As a result, the code becomes unwieldy and oversaturated with if statements branching out in all sorts of directions.
How to avoid this mistake:
It's easy to do by implementing the function detection in the code, not in the browser. This will significantly reduce the amount of code and will be much easier and more enjoyable to read.
5) Code that should work but doesn't work
You've created and tested JavaScript or code, and it looks like everything will work fine after deployment. But this is not the case. Some sites do not check for errors with sufficient quality and disclose them to users in an ugly way.
How to avoid this mistake:
All people are wrong, so take this as a philosophy and in coding. As you develop your code, implement good error trapping and error detection techniques. For example, to create robust code that will withstand all future changes, use unit testing.
SUM UP
Mistakes happen to everyone, and that's okay. The main thing is to learn to identify them and understand their influence. By taking steps to prevent errors, you can create a correct development process.