say I have an array that I want to sort, that a certain element will be first, and leave the rest the way it is.
for example [1,2,3,4] and I want the 2 to be at the beginning of the array
[1,2,3,4].sort((a,b)=> a == 2 ? -1 : 0)
in chrome the output is as expected
// chrome
[2,1,3,4]
but in Firefox the output is different and the 2 is not first
// firefox
[1,2,3,4]
You also need to handle the cases were b is 2 properly:
.sort((a, b) => (b === 2) - (a === 2))
but in Firefox the array is not sorted
Not quite, Firefox might use a different sorting algorithm, such that the sorter is called with different arguments in a different order. The array is only sorted correctly in all different implementations if the following conditions are always true:
sorter(a, a) === 0
sorter(a, b) === - sorter(b, a)
Note that sorting is usually O(n log n) average case (though it could be better if a lot of elements are equal), whereas the problem can be solved in O(n):
const withoutTwo = array.filter(it => it !== 2);
const result =
Array.from({ length: array.length - withoutTwo.length }).fill(2)
.concat(withoutTwo);
false - false === 0 and according to developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… "If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. Note: the ECMAScript standard only started guaranteeing this behavior in 2019, thus, older browsers may not respect this.", right?
sorter(a, b) === - sorter(b, a) should probably be sign(sorter(a, b)) === - sign(sorter(b, a)) ;)[1,2,3,4].sort((a,b)=> a == 2 ? -1 : (b==2 ? 1 :0))
2.sortdifferent outcomes can and will happen.