(With the increasing complexity and diversification of Web services, improving front-end efficiency has been regarded by many front-line enterprises as the key optimization direction at the technical level. In the interview, the understanding of efficiency engineering and the optimized output in practice have also become common standards to measure the ability of front-end engineers. For any front-end practitioner, the ability to optimize efficiency can not only provide help for interview and promotion, but also precipitate the long-term value of the front-end practitioner's career. The column combs the knowledge points and cases related to efficiency improvement in the front-end development workflow, builds a systematic front-end efficiency knowledge system for you, establishes correct problem-solving ideas, and makes your efficiency based on optimization.)