Technically not if packages are just the misguided habit of "one package per function" seen in the Node ecosystem. Same amount of code, increased amount of complexity/meta-problems to deal with.
No. Using a package for a single function doesn't preclude code reuse.
Look at underscore.get package. You could write your own recursive key finder (which I have before), and so could every package author, and you'd have 10x the amount of implementations of a recursive key finder.
A single require of underscore.get by you and other authors means you have a single, well tested implementation with a million other users rather than 10 low quality ones.
const {get} = require("underscore.get");
get(obj, 'a[0].b', defaultValue);
Exactly. If it's a difficult line of code, with edge cases, requiring unit tests, etc. then sure. Algorithms are a great example of this.
Using your own example: how many badly written copies of https://github.com/NarHakobyan/underscore.get/blob/master/un... do you want?