SOURCE

var v = document.getElementById('val')
var q = document.getElementById("qrcode")
document.getElementById('btn').onclick = function(e){
    q.innerHTML = ''
    var qrcode = new QRCode(q, {
        text: v.value||"https://www.example.com",
        width: 512,
        height: 512,
        colorDark : "#000000",
        colorLight : "#ffffff",
        //correctLevel : QRCode.CorrectLevel.H
    });
    //获取画布
    var canvas = qrcode._oDrawing._elCanvas, ctx = canvas.getContext('2d');
    //获取画布二进制数据
    var dt = ctx.getImageData(0,0,canvas.width,canvas.height);
    //解码
    var r = jsQR(dt.data,canvas.width,canvas.height);
    console.log('qr',r.data)//r.data
}
//https://blog.csdn.net/2301_80232843/article/details/149206921 生成
//https://www.cnblogs.com/geekcjj/p/18352006 解码

<div>
    <textarea id="val" cols="50" rows="10">123</textarea>
</div>
<div>
    <button id="btn">生成二维码</button>
    <div id="qrcode"></div>
</div>