Pull spreadsheet data from Google Sheets into React web app

ReactJS is a front-end library for JavaScript. You could integrate the Sheets API into that same JavaScript project. Please check the API quickstart to see an example credentials flow. Once that example is integrated in the project, you could develop your own functions to work with Sheets. A way to pull data from a sheet is to use the method spreadsheets.values.get. To get all the data, you only have to fill the range parameter with your sheet name.