You can't do it client side and expect it to always work. If it is important check on the server side too, else people will use modified copies of the form or other client side means to upload oversize files.
Server side checks are like a lock, client side checks are like a post-it note that says "keep out". Lock the door first, then put up the "keep out" sign. If the client doesn't just simply state that the site requires javascript to be enabled.
Javascript has a file reader that essentially cant be tricked, it reads bit by bit so there is no worry about receiving a small file that is secretly another size. Server side is the preferred "secure" method, but i don't see how javascript isn't just as secure when talking about file size. Because like user said Javascript can be easily modified whatever you do. You can do this on top of the server side check for usability, but you can't secure it with client side Javascript.
Using just JavaScript client-side code is not feasible as it can be easily bypassed. A server-side logic is needed. While the server side should always do final validation, doing it on the client side as well will limit the number of bad uploads from anyone not looking to bypass the checks and having Javascript enabled - this will generally represent the vast number of users, if you are implementing both user facing and server portions.
Show 2 more comments. Haseeb Rehman Haseeb Rehman 1, 1 1 gold badge 7 7 silver badges 11 11 bronze badges. AkshayAnurag client side validation prevent wasting time of the client and bandwidth of the server,its not about security its about the UX — Arash Moosapour. AkshayAnurag you can only check image size on backend after the whole image is uploaded and if that is a huge image, lets say 16mb and client have a slow connection than user will have to wait the whole time the image is uploading just to get an error at the end.
To prevent something like that you need some sort of validation on front-end. Please do let me know if I am wrong or missing something or maybe you have something to prevent this? AkshayAnurag If " there are better ways of doing it ", you should post your own answer. You can't do it client-side. You'll have to do it on the server. Edit: This answer is outdated! Ortiga Ortiga 8, 5 5 gold badges 40 40 silver badges 66 66 bronze badges.
Yes, it's impossible right now. There are some drafts of a new file api in HTML5, but no browser fully support it at the moment. See: cs. You don't have access to the local file system on a visitors computer, the best you can hope for is to have apache limit the file size and stop the upload if it is too large.
It's stupid to do it on the client side - unless you just want to make it convenient for the user. You may validate client side. Show 1 more comment. This is a demonstration of client-side validation and is implemented to provide a nice user experience. In some cases, client-side validation is a much better method in comparison to the server-side method as it consumes less time.
Approach Listen for the change event on the input. Check if any file is selected files. Get the size of the file by files. The value will be in bytes.
Convert it into any unit as you desire, Megabytes in this case by Math. Check if the size follows your desired criteria. Listen for the change event on the input. Get the size of the file by this. You can round off the obtained value as well by toFixed method. Skip to content. Change Language. Find centralized, trusted content and collaborate around the technologies you use most. Connect and share knowledge within a single location that is structured and easy to search.
But this says that the file should be exactly kb big. How can I edit this rule so that it returns an error when it's bigger than kb? The field under validation must have a size matching the given value.
For string data, the value corresponds to the number of characters. For numeric data, the value corresponds to a given integer value. For files, size corresponds to the file size in kilobytes. According to the documentation :.
Edit: Warning! My file upload field is named 'upload' so I was getting "The upload failed to upload. This message comes from this line in validation. So instead, as a super-dodgy-hack, I chose to get into my view that displays the messages and replace that specific message with my friendly 'file too large' message. In case anyone else is using Laravel FormRequest class, here is what worked for me on Laravel 5. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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