Error in Javascript while trying to access element from array

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?

Don't know if this is the cause, but I think x / 10 should be (x - x%10) / 10. — GolezTrol
– GolezTrol, Commented Jul 29, 2015 at 17:43
others gave the answer already except that you've also misunderstood how Javascript's for works - need to do something like: var i = bomb_list[x] in that loop. i made a jsfiddle where debugged & fixed this too, with that and Math.floor: jsfiddle.net/sg9dgpr0 — antont
– antont, Commented Jul 29, 2015 at 18:03

GolezTrol · Accepted Answer · 2015-07-29 17:55:53Z

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.

edited Jul 29, 2015 at 17:55

GolezTrol

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answered Jul 29, 2015 at 17:42

vilsad

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1 Comment

GolezTrol Over a year ago

Math.floor is the right one. x/10 to get the row is slightly to large, because x also contains the cell on that row. Math.floor rounds down, which is what you want in this case. B.t.w, it's floor and ceil in lowercase.

Ivan · Accepted Answer · 2015-07-29 17:42:20Z

1

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;
}

answered Jul 29, 2015 at 17:42

Ivan

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1 Comment

GolezTrol Over a year ago

Math.floor would be the most obvious, since it is float. parseInt will first convert the float to string and then try to parse that string to an int.

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