Random number generator to not generate same number

im creating an mines game in javascript in which i generate an random number that is assigned to an div an this div will be an mine, but the problem is that for e.g ( i set the number of mines to 8, instead of getting 8 different mines i get 8 mines but like 2 of them are in the same place so it counts as if i had 6 mines, how can i fix it? here is the important part of the codem, also any tip on how to improve in my code it will be appreciatted as im very new to program)

let tiles = document.getElementsByClassName('tile');
let numMines = 6

for (i = 0; i < 1; i++) {
    bomb = [tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))],
    tiles[(Math.floor(Math.random ()* tiles.length))]]
    bomb.splice(numMines) 


    bomb[0].style.backgroundColor = "red"; 
    bomb[1].style.backgroundColor = "red";  
    bomb[2].style.backgroundColor = "red";
    bomb[3].style.backgroundColor = "red"; 
    bomb[4].style.backgroundColor = "red";  
    bomb[5].style.backgroundColor = "red";
    bomb[6].style.backgroundColor = "red"; 
    bomb[7].style.backgroundColor = "red";  
    bomb[8].style.backgroundColor = "red";
    bomb[9].style.backgroundColor = "red"; 
    bomb[10].style.backgroundColor = "red";  
    bomb[11].style.backgroundColor = "red";
    bomb[12].style.backgroundColor = "red";
    bomb[13].style.backgroundColor = "red"; 
    bomb[14].style.backgroundColor = "red";  
    bomb[15].style.backgroundColor = "red";
    bomb[16].style.backgroundColor = "red"; 
    bomb[17].style.backgroundColor = "red";  
    bomb[18].style.backgroundColor = "red";
    bomb[19].style.backgroundColor = "red";  
    bomb[20].style.backgroundColor = "red";
    bomb[21].style.backgroundColor = "red"; 
    bomb[22].style.backgroundColor = "red";  
    bomb[23].style.backgroundColor = "red";
    bomb[24].style.backgroundColor = "red"; 
    bomb[24].style.backgroundColor = "red";   
} ```