手机端js图片上传裁剪

<input type="file" id="imageUpload" accept="image/*">
<img id="imagePreview" src="#" alt="Image Preview">

document.getElementById('imageUpload').addEventListener('change', function(event) {
    var file = event.target.files[0];
    var reader = new FileReader();
    reader.onload = function(e) {
        document.getElementById('imagePreview').src = e.target.result;
        var cropper = new Cropper(document.getElementById('imagePreview'), {
            aspectRatio: 16 / 9,
            autoCropArea: 0.8,
            guides: false,
            center: false,
            highlight: false,
            cropBoxMovable: false,
            cropBoxResizable: false,
            dragMode: 'move',
            viewMode: 3
        });
    };
    reader.readAsDataURL(file);
});