sort function is required to return a stable value

[normanr]

The function passed to sort is supposed to return the same value when given a specific pair of elements a and b as its two arguments (ref: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Description)

prefix = prefix.split('').sort(function(){return 0.5-Math.random()}).join('')

does not meet this requirement. https://medium.com/@nitinpatel_20236/how-to-shuffle-correctly-shuffle-an-array-in-javascript-15ea3f84bfb has some commentary on why this is bad.

does not meet this requirement. https://medium.com/@nitinpatel_20236/how-to-shuffle-correctly-shuffle-an-array-in-javascript-15ea3f84bfb has some commentary on why this is bad.

There are various ways to do it correctly, either Fisher–Yates or the "assign a random number to each element" method. The former is more efficient (and doesn't have a problem if the function returns the same value twice), but the latter is shorter to implement in javascript (and the number of input elements so low that it practically doesn't matter):

prefix = prefix.split('').map(x=>[Math.random(),x]).sort().map(x=>x[1]).join('');

or non ES6 syntax:

prefix = prefix.split('').map(function(x){return[Math.random(),x]}).sort().map(function(x){return x[1]}).join('')