You can learn from React JS documentation by React and in case of queries, you can get help from the online community. There are a lot of free online resources and blogs to learn React JS. After learning React JS, start building small applications like a to-do app, calculator, online shopping cart, etc. For certification, you can enroll an online course for React JS that provides good hands-on experience of React JS.
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You can watch this video on React JS course for beginners to get a quick start with React JS: