A few extra resources for those geared towards front-end development and/or design:
Side note: whiteboarding and coding challenges are common no matter what the stack.
A technical interview, or technical portion of an interview, will focus on your coding knowledge and problem solving skills. The purpose is to get an idea of how you think, and what strengths you can bring to their company.
A technical interview is, for many, the most stressful part of the job-hunting process. Coding is hard enough on your own or with a pair, but now you're going to be asked to solve coding and pseudo-coding problems in front of potential employers. The key is to practice before the real thing, so you're not too nervous when you're in the real thing.
Job interviews can take many formats. Some employers will conduct a pairing interview, where you'll pair program with your interviewer. Sometimes this will be on a standard problem the employer uses to evaluate candidates; sometimes it will be on real work that the employer has; and occasionally they may ask you to pair on one of your own projects. This is an excellent interview format, as it tests what you'll actually be doing on the job, and doesn't really require any special prep. Unfortunately, only a minority of employers use this format.
The more difficult interviews will involve answering technical questions out loud, or "whiteboarding" a solution to a coding problem - sketching out a visual and/or pseudo-code solution to a problem, and talking out loud about your thought process as you go. This is one of the most common interview formats, and where you should spend a good amount of extra time preparing.
There are three things you should make sure to do when you get an in-person technical question:
An excellent practice method for this type of question is to find a resource for code challenge questions, and practice talking out loud while you solve the problem. You can do this while writing the answer on a sheet of paper, or even with a dry-erase marker on the bathroom mirror. The main practice point is to write the code by hand, and explain what you're doing while you're doing it. Here are some sample challenges to work on from CoderByte. You can find many additional sample code challenges online.
strparameter being passed and return the string in reversed order.
numparameter being passed and return the factorial of it (ie. if num = 4, return(4 * 3 * 2 * 1)). For the test cases, the range will be between 1 and 18.
strparameter being passed and modify it using the following algorithm. Replace every letter in the string with the letter following it in the alphabet (ie. c becomes d, z becomes a). Then capitalize every vowel in this new string (a, e, i, o, u) and finally return this modified string.
Another type of question you get in a technical interview may not require you to code at all. These questions may come in addition to a code question, and are open ended discussion questions designed to give you a chance to showcase your knowledge. It's important to take advantage of these opportunities, as you have the freedom to highlight your strongest area of knowledge.
Here are some sample interview questions. (adapted from hiringthing) Practice answering these questions, and consider how the answers could form excellent talking points as you work through a technical coding question.
Here are the React Specific Interview Prep Questions