$("#run").click(run);
function run(){
Excel.run(function (ctx) {
    var chart = ctx.workbook.worksheets.getItem("Sheet1").charts.getItem("Chart 1");
    var image = chart.getImage();
    return ctx.sync().then(function () {
        var srcImage = "data:image/png;base64, " + image.value;
        $("#chart").attr("src", srcImage);
    });
}).catch(function (error) {
    console.log("Error: " + error);
    if (error instanceof OfficeExtension.Error) {
        console.log("Debug info: " + JSON.stringify(error.debugInfo));
    }
});
}



<p class="ms-font-m">Shows the chart image below</p>
<button id="run" class="ms-Button">
    <span class="ms-Button-label">Run code</span>
</button><br/>
<img id="chart" src="" alt="" />