Vue.js, as the Data-driven front-end framework, stands out as one of the mainstream choices for front-end developers. This book provides a detailed introduction of Vue.js framework design principles, including an overview of framework design, response systems, renderers, componentization, compilers, and server-side rendering. Based on Vue.js 3 and strict compliance with the specifications, this book starts from source code with a large number of visual diagrams combined, explaining the implementation of each functional module in Vue.js step by step. By reading this book, developers with hands-on experience with Vue.js 2/3 will be able to further understand the implementation details of Vue.js framework, while front-end developers who are not experienced in vue.js but interested in framework design can quickly grasp the design principle of vue.js.