合成图片并下载

window.onload = function () {
        document.getElementById('saveAs').addEventListener('click', function () {
            var box = document.getElementById('poster')
            html2canvas(box, {
                useCORS: true,
                allowTaint: true,
                taintTest: false,
                scrollX: 0,
                scrollY: 0,
                backgroundColor: 'transparent'
            }).then(canvas => {
                const el = document.createElement('a')
                el.download = new Date().getTime()
                el.href = canvas.toDataURL('image/png')
                el.click()
            }).catch(e => {

            });
        })
    }