I love this solution! I'm kinda obsessed with reduce() and I've lost my ability to see other solutions,if I can use reduce(). How to overcome that >< ???

The best one for sure.

good to know people with great cleverness!

Your solution is not displayed completely. Please, train this kata again and include the other foo's into scramble()

Performance and simple!

So why do you map the characters in the first string, which can potentially be very big, than doing it on the 2nd one ? It helps with performance in average cases.
str2 will aways be shorter than str1 otherwise the function returns false

e.g
str1 has 1million characters
str2 has 5 characters
str2 can be made out from the first 10 characters of str1
you have just saved a lot of space if you also keep track of when keys in the map reach 0.
Check my solution for how to get max performance for this.

You should use the newer ES6 version for (let ch of str1) because that will not iterate over inherited properties.

在计算大量数据时，还是这种方法靠谱。

Good thing that you return a new array insted of mutating the given one !

Great solution!

it returns true even for strings which are not JoJo, for example "jorg aajobb".