Array.from TypeError: 0 is not a function

map calls its callback with three arguments: The entry, the index, and the object being iterated over. Array.from expects that if a second argument is given to it, it's a mapping function, and so tries to call it on each "element" it's building the array out of. The index, 0 on the first call, isn't a function, so Array.from fails.

Put it another way, the equivalent of

['test'].map(fn)

is not

['test'].map(e => fn(e))

but rather

['test'].map((e, i, a) => fn(e, i, a))

...where e is the entry, i is its index, and a is the "array" being traversed by map. Since i is not a function, Array.from fails.

You get the same sort of thing with several other array functions, such as forEach, some, ...

---

If you do this a lot, you may find it useful to have a function you can use to filter all but the first argument:

function passOneArg(f) {
    return function(a) { return f.call(this, a); };
}

which you can use like this:

['test'].map(passOneArg(fn))

Or possibly even

function limitArgs(f, count) {
    return function() {
        return f.apply(this, Array.prototype.slice.call(arguments, 0, count));
    };
}

then

['test'].map(limitArgs(fn, 1))

Those are, of course, two of the worst function names on the planet, but you get the idea... :-)