UX rules you must know as a Frontend/Fullstack developer

As a modern frontend developer sometime you may not have any dedicated designer for the project. Without a designer, a front-end/full-stack developer can definitely build the application with the help of libraries but this approach has certain drawback on UX quality.
First of all, UX is different than UI.

UI = “How it looks like”
UX = “What it feels like”
Knowing Ux rules are a must-have requirement for a successful frontend developer.
Below I have mentioned some UX laws/rules. I have simplified them for easy understanding.
Aesthetic Usability Effect
Aesthetic beautiful design can boost user experience. “User more likely forgive minor usability issue if your product is beautiful”

Doherty Threshold
User likes product which has response time not more than 400 milliseconds. When a user commands something and returns under 400m.sec, user tend to addict to that experience.
Fitts’s Law
The amount of time taken move cursor and select an element is a function of the distance to and size of the target. If you want to make an action more easily/rapidly selectable move it closer to the user and make it larger than other elements.

Hick’s Law
More option user presented with, more time it will take them to make a decision. Use this depends on your used case. sometime, you may need user stay longer and sometime you will need a quick decision.
Jakob’s Law
Users want similar experience through their experience. As an example, we all use the floppy disk icon for indicating something to save, this follows Jakob’s Law.
Law of Common Region
Objects that share an area with a boundary will be visually grouped together. The best example is a card component.
Law of Prägnanz
People will perceive and interpret complex images as the simplest form possible because it is the interpretation that requires the least cognitive effort of us.
Use the simple but effective graphical design for the product. User loves simple.
Law of Proximity
Elements those place near, will visible as a group to the user. Modern forms are following this rule. Input fields are placed near to each other.
Miller’s Law
A normal user can only keep a max 7 item in their working memory. Organize 5–9 content on viewport each time.
Pareto Principle
The Pareto principle states that, for many events, roughly 80% of the effects come from 20% of the causes. Focus the majority of the effort on the areas that will bring the largest benefits to the most users.
Peak-End Rule
People judge an experience largely based on how they felt at its peak and at its end, rather than the total sum or average of every moment of the experience. Pay close attention to the beginning and end of pages.

There are also some few UX rules, but I think these are the most useful and important.
Thank you for your time, feel free to reach me out. :)