Randomly selecting unique items from an array with Javascript

I know that there have been a lot of similar questions and I went through most of them. The code that is closest to what I'm trying to achieve is this one. I have a list of people in each column (which represent a day). for the sake of this question let's assume it's 8 people in each column. I need to randomly select 5 unique people names. I've used splice() to delete the selected item from the array to make sure that it is not selected twice. I'm new to the coding and I think I'm doing some basic mistake as the splice works for the 1st loop and then the array goes back to the original one. Can you, please, help to identify my mistake?

for (var x = 0; x < 5; x++) {
var sourceArray = ss.getRange(49,j+5,8,1).getValues();
var gg = Math.floor(Math.random()*sourceArray.length);
var pickedHLA = sourceArray[gg];
sourceArray.splice(gg, 1);
var HLAselect = ss.getRange(30+x,j+5,1,1)
HLAselect.setValue(pickedHLA);