Javascript canvas.toDataURLWithMultiplier不是函数

我正在尝试导出画布大小为4倍的图像

与

我将图像设置为画布的大小

然而当我尝试

var dataURL = canvas.toDataURLWithMultiplier(4);

我得到错误canvas.toDataURLWithMultiplier不是一个函数

下面是我的函数

$('.preview').on('click touchstart', function() {

  // save canvas image as data url (png format by default)
  canvas.isGrabMode = false;
  canvas.setZoom(1.0);
  canvas.viewportTransform = [1, 0, 0, 1, 0, 0];
  // var dataURL = canvas.toDataURL();

  var dataURL = canvas.toDataURLWithMultiplier(4);
  // so it can be saved as an image
  document.getElementById('previewImg').src = dataURL;

  canvas.renderAll();

});

在中使用乘数属性

$('.preview').on('click touchstart', function() {

  // save canvas image as data url (png format by default)
  canvas.isGrabMode = false;
  canvas.setZoom(1.0);
  canvas.viewportTransform = [1, 0, 0, 1, 0, 0];
  // var dataURL = canvas.toDataURL();

  var dataURL = canvas.toDataURLWithMultiplier(4);
  // so it can be saved as an image
  document.getElementById('previewImg').src = dataURL;

  canvas.renderAll();

});

var dataURL = canvas.toDataURL({
  format: 'png',
  multiplier: 4
});