尝试从数组访问元素时Javascript错误

Question

I'm working on a MineSweeper program, and here's my problem:

So I make a 10x10 grid full of MineSquare objects which I defined earlier.

var grid = [];
    for (var i=0; i<10; i++){
        grid.push([]);
        for (var j=0; j<10; j++){
            grid[i].push(new MineSquare())
        }
    }

Then I make an array "bomb_list" to create 20 unique locations where the bombs will be.

var bomb_list = [];
var found;
var rand;
while (bomb_list.length < 20){
    found = false;
    rand = Math.floor(Math.random() * 100);
    for (var i=0; i<bomb_list.length; i++){
        if (bomb_list[i] === rand){found=true; break;}
    }
    if(!found){
        bomb_list.push(rand);
    }
}

Then I try to change the value of those MineSquare's to indicate they are bombs.

for(var x in bomb_list){
    grid[ x / 10 ][ x % 10 ].touching = -1;
}

I am getting an error that says "Uncaught TypeError: Cannot read property '1' of undefined" which I believe is being caused when I try to take grid[x / 10].

Any reason why this is occuring?

Answer 1

X/10 will give you a float value, should use Math.ceil or Math.floor to get the nearest int as per your logic. Then it should work.

Answer 2

x/10 will produce a float. When x is 1 , it will be 0.1 . There is no index in grid of 0.1 , so the result is undefined . That is why you get that error.

You can Math.floor or parseInt depending on what you are trying to do:

for(var x in bomb_list){
    grid[ parseInt(x / 10) ][ x % 10 ].touching = -1;
}