Return N unique random numbers in JS array

Question

I am going to do small game like Google Mineshweeper on JS. And I need to write function, that gets amount of numbers N and returns N unique random numbers in array. It's easy to do array with repeating, but I can't understand, how to create array without it. I use this code to initialize game field:

const game = {
    init: function(fieldWidth, fieldHeight, fieldBombs) {
        let field = [];
        let bombsPos = [];
        for (let i = 0; i < fieldWidth * fieldHeight; i++) {
            field[i] = {
                isBomb: false,
                nearbyBombs: 0,
            }
        }

        for (let i = 0; i < fieldBombs; i++) {
            // It's possible to repeat numbers!!!
            bombsPos[i] = Math.floor(Math.random() * (fieldWidth * fieldHeight)); 
            field[bombsPos[i]].isBomb = true;
        }
        return field;
    },
    reset: function() {
        // Other code
    }, 
}
console.log(game.init(2, 2, 2));

So, can you help me to solve this problem? Thanks in advance.

Answer 1

Use a while loop instead, while the bombsPos array length is smaller than the fieldBombs number:

while (bombsPos.length < fieldBombs) {
    const index = Math.floor(Math.random() * (fieldWidth * fieldHeight));
    if (!field[index].isBomb) {
        field[index].isBomb = true;
        bombsPos.push(index);
    }
}

const game = {
    init: function(fieldWidth, fieldHeight, fieldBombs) {
        let field = [];
        let bombsPos = [];
        for (let i = 0; i < fieldWidth * fieldHeight; i++) {
            field[i] = {
                isBomb: false,
                nearbyBombs: 0,
            }
        }
        while (bombsPos.length < fieldBombs) {
            const index = Math.floor(Math.random() * (fieldWidth * fieldHeight));
            if (!field[index].isBomb) {
                field[index].isBomb = true;
                bombsPos.push(index);
            }
        }
        return field;
    },
    reset: function() {
        // Other code
    }, 
}
console.log(game.init(2, 2, 2));

But it looks like you aren't using the bombsPos array. Is that deliberate, or a mis-copy from your actual code? If you really aren't using it elsewhere, then use a Set of the indicies found so far instead.

const game = {
    init: function(fieldWidth, fieldHeight, fieldBombs) {
        const field = [];
        const bombIndicies = new Set();
        for (let i = 0; i < fieldWidth * fieldHeight; i++) {
            field[i] = {
                isBomb: false,
                nearbyBombs: 0,
            }
        }
        while (bombIndicies.size < fieldBombs) {
            const index = Math.floor(Math.random() * (fieldWidth * fieldHeight));
            if (!field[index].isBomb) {
                field[index].isBomb = true;
                bombIndicies.add(index);
            }
        }
        return field;
    },
    reset: function() {
        // Other code
    }, 
}
console.log(game.init(2, 2, 2));