首先,在html上定义画布：

<canvas id="connection-canvas"></canvas>

然后你可以在上面划一条线：

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();
}

你需要的只是弄清楚你的“圆形指针”的偏移量：

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

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

因此,您可以使用这两个函数获取“圆形指针”的中心点并在画布中绘制一条线从另一个“圆形指针”,假设画布位于相同的答案容器的偏移父级及其大小必须足够大.

接下来,您必须处理选择两个连接它们的答案.下面有一个演示版.如果您更改答案,此演示不会处理删除行.

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: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>