问题
In html form, we have a image field, to upload a file. I followed tutorial from http://blog.teamtreehouse.com/reading-files-using-the-html5-filereader-api and it works fine when uploading a image file from local disk.
But suppose i have a image url say http://www.google.com/images/logos/ps_logo2.png and want to upload this image from remote url instead of uploading from local disk.
FileReader API works well when trying upload image from local disk but how can we use it to load images by urls?
Its easy to create a base64 of image and use it for preview by setting in image field as <img src='data:image/png;base64,iAks4ds__base64__string' id='user_img'> but what workflow should one adopt to upload images from remote url using jQuery or JavaScript?
How can i? Any suggestions?
回答1:
FileReader API is dedicated to local files (cf http://www.html5rocks.com/en/tutorials/file/dndfiles/)
If you want to download an image from a remote URL and extract its data in javascript you can use Image and Canvas elements, as explained in the following question: Convert an image into binary data in javascript
回答2:
as @fiddler answer says, fileReader is for local files only,
if you need to get things like images from remote urls, then you may follow another approach
1) using Http Get request
2) using Canvas features
but due to security threat, browsers not allow scripts to do cross origin requests, only DOM itself can do that. that can be solve by
1) Cors (Cross-Origin Resource Sharing) ?
2) Jsonp ?
now you curious so cors or jsonp
if you have access to server where your remote things exist you can do server side cors ?, which is recommended by most.
but as question looking for a solution which can handle any remote resources, cors proxy ? help you
free cors proxies
来源：https://stackoverflow.com/questions/20903812/how-to-upload-image-file-from-url-using-filereader-api