Ich habe 2 Zeilen zwischen 2 DIVs erstellt, sobald der Benutzer auf die DIVs geklickt hat. Jetzt habe ich ein Problem damit, wie ich die unerwünschte Leitung zurücksetzen kann, wenn ich meine Antwort ändern möchte.

Sie können meinen aktuellen Code für Ihre Referenzen sehen:

var lastSelection;

// Add click listener for answer-container
function listenToClick() {
    var rows = document.querySelectorAll('.row'),
        row;
    var cols, col;

    for (row = 0; row < rows.length; row++) {
        cols = rows[row].children;

        for (col = 0; col < cols.length; col++) {
            // Bind information about which answer is this,
            // so we can prevent from connecting two answers on
            // same column.
            cols[col].addEventListener('click', selectAnswer.bind({
                row: row,
                col: col,
                element: cols[col]
            }));
        }
    }
}

// This is fired when a answer-container is clicked.
function selectAnswer(event) {
    if (lastSelection) {
        lastSelection.element.classList.remove('selected');
    }

    if (!lastSelection || lastSelection.col === this.col) {
        lastSelection = this;
        this.element.classList.add('selected');
    } else {
        drawLine(getPoint(this.element), getPoint(lastSelection.element));
        lastSelection = null;
    }
}

function getPoint(answerElement) {
    var roundPointer = answerElement.lastElementChild;

    return {
        y: answerElement.offsetTop + roundPointer.offsetTop + roundPointer.offsetHeight / 2,
        x: answerElement.offsetLeft + roundPointer.offsetLeft + roundPointer.offsetWidth / 2
    };
}

function drawLine(p1, p2) {
    var canvas = document.getElementById("connection-canvas");
    var ctx = canvas.getContext("2d");

    ctx.beginPath();
    ctx.moveTo(p1.x, p1.y);
    ctx.lineTo(p2.x, p2.y);
    ctx.stroke();
}

function resizeCanvas() {
    var canvas = document.getElementById("connection-canvas");
    var ctx = canvas.getContext("2d");

    ctx.canvas.width  = window.innerWidth;
    ctx.canvas.height = window.innerHeight;
}

listenToClick();
resizeCanvas();

.padding-answer-line-mapping
{
    padding-bottom:8px;
}

.answer-container
{
    width:40px;
    height:40px;
    background-color:#ccc;
    border:1px solid #ccc;
    margin:2px;
    float:left;
    text-align:center;
    padding-top:8px;
    cursor:pointer;
    position:relative;
}

.answer-container:hover, .answer-container:focus, .answer-container:active
{
    background-color: #0076e9;
    color: white;
    border: 1px solid #0076e9;
}

.round-pointer-right
{
    position: absolute;
    background-color:#ccc;
    cursor:pointer;
    width:10px;
    height:10px;
    border-radius: 50%;
    right:0px;
    top:14px;
    margin-right:-20px;
}

.round-pointer-left
{
    position: absolute;
    background-color:#ccc;
    cursor:pointer;
    width:10px;
    height:10px;
    border-radius: 50%;
    left:0px;
    top:14px;
    margin-left:-20px;
}

.selected {
    background-color: red;
}

<link href="//code.ionicframework.com/1.3.1/css/ionic.css" rel="stylesheet"/>
Match the following items.

 <canvas id="connection-canvas" style="position: absolute; top: 0; left: 0; right: 0; bottom: 0"></canvas>
<div class="row padding-answer-line-mapping">
    <div class="col answer-container">
        One
        <div class="round-pointer-right"></div>
    </div>
    <div class="col">
        
    </div>
    <div class="col answer-container">
        2
        <div class="round-pointer-left"></div>
    </div>
</div>
<div class="row padding-answer-line-mapping">
    <div class="col answer-container">
        Two
        <div class="round-pointer-right"></div>
    </div>
    <div class="col">
        
    </div>
    <div class="col answer-container">
        1
        <div class="round-pointer-left"></div>
    </div>
</div>