Some tips from somebody that has done lots of interviews and has also interviewed others:
* Use technologies they have in their stack. There are websites that help you find out what technologies companies are using to build their product. For client side code it's not very hard to find out by yourself, look at the source, look at the libraries that get loaded, beautify their code and have a look at what gets imported. Try to find out if they use react, backbone, angular or something else ... when you have found out, use those libraries for your project. When building your project use as much of those technologies to show them that you are familiar with the technologies they use.
* Make something related to the company you want to apply to, if you want to work for a game company, don't make a blog about cooking recipes, make a game ;). Try to find the idea for a tool that does something that is related to their business. Show then that you have taken the time to look into what they do. Maybe that prototype you have created will be so impressive that they may want to transform it into a real project after hiring you.
* If they have an API, use their API to get data for your project. Don't do a project that uses dummy date. Use their API and try to create something new using their data. Use the data they use for their product but display it in a different way, to show that you thought about what can be done with that data. So copy or create a page or tool they already have but try to innovate using their API. Or even better do a mashup. Combine their API with another one to create something new that is more spectacular than just using their data. Or if you can, grab their data and enhance it, for example by sorting it using some intelligent algorithm.
* Not that important but always worked well for me ... make something fun :) Try to avoid making a tool that is boring. For example let's say you want to apply at twitch, then don't just make a page that lists the top ten streamers, but make a page where people enter the name of two streamers and then a dust cloud appears with some fighting sounds and after your code has compared the stats of both streamers, a winner gets displayed. Ok this is not super fun ;) but it's an example, I guess you get the idea. If the people that review you, have a smile on their face while testing your project, it's a good thing and will help them remember you.
* Also not so important, but it can still make the difference, try to make something beautiful. Don't just apply some basic css rules to your project. Yeah developers will tell you the most important is code quality, but I'm sure that some good code that outputs something beautiful, will always be better than just some good code. People and even developers ;) also judge with their eyes. People might be unconscious of it, but I'm sure something that looks good, helps to give the feeling that it is actually good. If you don't have the skills yourself to make your project look good, than ask a friend to help or ask somebody on the web to help you.