It is a creational design pattern that is used to construct complex objects step-by-step. It helps in creating different representations of an object with numerous configuration options.
you’re building an application where users have highly configurable profiles. A user profile may include optional attributes like contact information, roles, permissions, preferences, etc. It makes for better design to use builder pattern to create a user with specific profile instead of having muliple contructors in a class or optional params to create one.
You need to build an API client builder that lets you configure multiple options like base URL, headers, timeout, and authentication separately before creating the final client instance.
Another example would be a SQL query builder where one needs to use multiple clauses (WHERE, SELECT, GROUP BY, etc). This pattern provides a structured way to construct these queries in a type-safe, extendable, and reusable manner. One such example is this Query Builder from Knex https://github.com/knex/knex/blob/master/lib/query/querybuilder.js#L329