在一个小方形 div 中添加数字

Question

this is a codepen demo at here and you try to click on the canvas and is able to undo and clear the grid. The problem I am trying to solve is I want to place some numbers (in black) in the red square. For example, when you click on the grid, first red dot will appear and inside labelled as 1 and the second will be labelled 2 and so on and if the dots overlap, it will just show the original number(not a new number). I have tried to use the code below:

var elements = document.getElementsByClassName('red-dot');    
  elements.innerHTML = 'Testing here';

Thank you for reading:)

Answer 1

This should do it:

• accessing elements by classname needs to be by index eg document.getElementsByClassName(.red-dot)[0] will access the first element with the classname red-dot
• in the codepen you used style top and left to position the red-dot, so i used it as skip if taken by an element of the same class name

The rest is self explanatory.

var elements = document.getElementsByClassName('red-dot');
    var eLength = elements.length;
    const dValue = parseInt(eLength) + 1;
    let isTaken = false;
    
    // check if dot number is taken
    for (let d=0;d<eLength;d++) {
      let top = elements[d].style.top;
      let left = elements[d].style.left;
      if (top == newDot.style.top && left == newDot.style.left) {
        isTaken = true;
      }
    }
    if (!isTaken) {
      newDot.dataset['dvalue'] = dValue;
      newDot.innerHTML = newDot.dataset.dvalue;
    } else {
      newDot.style.backgroundColor = 'transparent';
    }
    
    document.body.appendChild(newDot);