why javascript uses so much library functions even for the simple tasks ? can’t we just write those algorithms by ourselves in the program? [closed]

I have been practicing coding and DSA through C++. To overcome the monotonicity, I decided to learn the web technologies. While learning some of the topics in the JavaScript, like arrays for example, I encountered that there are so many library functions/ methods to perform even the basic operations in the array. I am curious if the people in the industry also use them or not ? and can’t I just write my own algorithms for those tasks ??