Question 184509 in Javascript Question posted in
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Javascript – Why is the first index empty?

When I try to create a new 2d array the first index is an empty array.

let gameState = {
    grid: [],
    playing: false,
};

for (let i = 0; i < 3; i++) {
  gameState.grid[i] = [];
  for (let j = 0; j < 3; j++) {
    gameState.grid[i][j] = {
      state: 0,
      pos: {
        x: i * 3,
        y: j * 3,
      },
      color: {
        r: 0,
        g: 200,
        b: 0,
      },
    };
  }
}

Not sure where its mutating, the debugger shows it correctly but if i try to access the element its empty.

Tried used an Array(3).fill(…)

Output

gameState.grid = [
  [],
  [{object},{object},{object}],
  [{object},{object},{object}],
]

Expected

gameState.grid = [
  [{object},{object},{object}],
  [{object},{object},{object}],
  [{object},{object},{object}],
]

DevTools output

{
  "grid": [
    [],
    [
      {
        "state": 0,
        "pos": {
          "x": 3,
          "y": 0
        },
        "color": {
          "r": 0,
          "g": 200,
          "b": 0
        }
      },
  // rest of the object
  ],
  "playing": false
}
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    Thanks everyone, Im a dumbass, I was changing the array someone else in the code and was throwing this error. Sorry and thank you.


  2. 0 
    let gameState = {
    grid: [],
    playing: false,
};

for (let i = 0; i < 3; i++) {
    // change to push here!
  gameState.grid.push([])
  for (let j = 0; j < 3; j++) {
    // change here
    const objectToPush = {
      state: 0,
      pos: {
        x: i * 3,
        y: j * 3,
      },
      color: {
        r: 0,
        g: 200,
        b: 0,
      },
    };
    // change to push here!
    gameState.grid[i].push(objectToPush);
  }
}

console.log("gameState is", gameState);
console.log("gameState.grid[0][0] is", gameState.grid[0][0])
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