The amount of JavaScript you need to learn for web development depends on your specific goals and ambitions within the field. Here's a breakdown based on different scenarios:

Basic Web Development:

Fundamentals: To build simple static websites with basic interactivity, a solid understanding of core JavaScript concepts like variables, data types, operators, functions, control flow, and DOM manipulation is essential. This might take 3-6 months of dedicated learning, depending on your prior programming experience.
Front-End Frameworks (Optional): If you aim for more dynamic and complex websites, consider popular frameworks like React, Angular, or Vue.js. However, mastering these frameworks requires a strong foundation in core JavaScript first.

Advanced Web Development:

Backend Development: Building web applications with server-side functionality demands mastering Node.js, which uses JavaScript in a different environment. Expect additional learning time, depending on your Node.js goals.
Full-Stack Development: Combining front-end and back-end skills requires expertise in both core JavaScript and its various application areas. This path involves significant dedication and time investment.

Remember:

Quality over Quantity: It's not just about the amount of code learned, but about understanding the concepts deeply and being able to apply them effectively.
Practice is Key: Build projects to solidify your knowledge and gain practical experience.
Continuous Learning: Web development is constantly evolving, so be prepared for ongoing learning throughout your career.
Here are some helpful resources to get you started:

Codecademy's Learn JavaScript course: https://www.codecademy.com/learn/introduction-to-javascript

The Odin Project's Full-Stack JavaScript curriculum: https://www.theodinproject.com/paths/full-stack-javascript

FreeCodeCamp's Responsive Web Design Certification: https://www.freecodecamp.org/learn/2022/responsive-web-design

I HOPE THIS HELPS YOU, COMMENT YOUR QUESTIONS.