I literally just got into this debate with a coworker yesterday. They didn't want lodash or immutable.js or any utility library in our new project at all, citing their size and the relative ease of doing it all natively. We use lodash or immutable or both in all our other projects but we always start out having these "purity" discussions until cooler heads prevail when we realize it's more important to optimize for convenience than it is to optimize for purity or even size. We're transpiling a future version of our language into an older version of our language just to get it to run, I think using lodash adding size is the least of our problems.