now many open source projects use small modules to develop, and finally package and merge multiple modules into a JS file, such as jquery, vue, react and so on. I would like to know what tools are used to complete this step? The most important thing is that the location of the code can be controlled after merging files, is it in the same way as the css preprocessor? Will it be merged automatically if it is imported directly in the specified location of the file?

trouble experienced friends to guide, or have learning materials, the situation is to ask Google do not know what word to search, I tried to search the JS module packaging tool, and did not find easy to understand the information first thank you for advice.