Html file select file types

Html file select file types

This produces the following output:

Note: You can find this example on GitHub too — see the source code, and also see it running live.

Regardless of the user’s device or operating system, the file input provides a button that opens up a file picker dialog that allows the user to choose a file.

Including the multiple attribute, as shown above, specifies that multiple files can be chosen at once. The user can choose multiple files from the file picker in any way that their chosen platform allows (e.g. by holding down Shift or Control , and then clicking). If you only want the user to choose a single file per , omit the multiple attribute.

When the example is submitted, each selected file’s name will be added to URL parameters in the following fashion: ?file=file1.txt&file=file2.txt

Getting information on selected files

The selected files’ are returned by the element’s HTMLInputElement.files property — this returns a FileList object, which contains a list of File objects. The FileList behaves like an array, so you can check its length property to get the number of selected files.

Each File object contains the following information:

• name : The file name.
• lastModified : A number representing the date the file was last modified, as a UNIX timestamp.
• lastModifiedDate : A Date object representing the date and time the file was last modified.
• size : A number representing the size of the file in bytes.
• type : A DOMString representing the MIME type of the file.

Limiting accepted file types

Often you won’t want any type of file. For example, if your file input lets users upload a profile picture, you probably want them to select web-compatible image formats, such as JPEG or PNG.

Acceptable file types can be specified with the accept attribute, which takes a comma-separated list of allowed file extensions or MIME types. Some examples:

• accept=»image/png» or accept=».png» — Accepts PNG files.
• accept=»image/png, image/jpeg» or accept=».png, .jpg, .jpeg» — Accept PNG or JPEG files.
• accept=»image/*» — Accept any file with an image/* MIME type. (Many mobile devices also let the user take a picture with the camera when this is used.)
• accept=».doc,.docx,.xml,application/msword,application/vnd.openxmlformats-officedocument.wordprocessingml.document» — accept anything that smells like an MS Word document.

Let’s look like a more complete example:

 
 
Choose file to upload 
Submit 
 

This produces a similar-looking output to the previous example:

Note: You can find this example on GitHub too — see the source code, and also see it running live.

It may look similar, but if you try selecting a file with this input, you’ll see that the file picker only lets you select the file types specified in the accept value (the exact nature differs across browsers and operating systems).

The accept attribute doesn’t validate the types of the selected files — it provides hints for browsers to guide users towards selecting the correct file types. It is still possible (in most cases) for users to toggle an option in the file chooser that makes all files selectable, and then choose incorrect file types.

Therefore, make sure that the accept attribute is backed up by appropriate server-side validation.

Examples

In this example, we’ll present a slightly more advanced file chooser that takes advantage of the file information available in the HTMLInputElement.files property, as well as showing off a few clever tricks.

Note: You can see the complete source code for this example on GitHub — file-example.html (see it live also). We won’t explain the CSS; the JavaScript is the main focus.

First of all, let’s look at the HTML:

 
 
Choose images to upload (PNG, JPG) 
No files currently selected for upload
 
 
Submit 
 

form < width: 95%; background: #ccc; margin: 0 auto; padding: 2.5%; >form ol < padding-left: 0; >form li < background: #eee; display: flex; justify-content: space-between; margin-bottom: 10px; list-style-type: none; >form img < height: 64px; order: 1; >form p < line-height: 32px; padding-left: 10px; >form label, form button < background-color: black; background-image: linear-gradient(to bottom, rgba(255, 0, 0, 0), rgba(255, 0, 0, 0.4) 40%, rgba(255, 0, 0, 0.4) 60%, rgba(255, 0, 0, 0)); color: #ccc; padding: 5px 10px; border-radius: 5px; border: 1px ridge gray; >form label:hover, form button:hover < background-color: #222; >form label:active, form button:active

This is similar to what we’ve seen before — nothing special to comment on.

Next, let’s walk through the JavaScript.

var input = document.querySelector('input'); var preview = document.querySelector('.preview'); input.style.opacity = 0;

Note: opacity is used to hide the file input instead of visibility: hidden or display: none , because assistive technology interprets the latter two styles to mean the file input isn’t interactive.

Next, we add an event listener to the input for when its selected value changes (in this case, when files are selected). The event listener invokes our custom updateImageDisplay() function.

input.addEventListener('change', updateImageDisplay);

Whenever the updateImageDisplay() function is invoked, we:

• Use a while loop to empty the previous contents of the preview .
• Grab the FileList object that contains the information on all the selected files, and store it in a variable called curFiles .
• Check to see if no files were selected, by checking if curFiles.length is equal to 0. If so, print a message into the preview stating that no files have been selected.
• If files have been selected, we loop through each one, printing information about it into the preview . Things to note here:
• We use the custom validFileType() function to check whether the file is of the correct type (e.g. the image types specified in the accept attribute).
• If it is, we:
  • Print out its name and file size into a list item inside the previous (obtained from curFiles[i].name and curFiles[i].size ). The custom returnFileSize() function returns a nicely-formatted version of the size in bytes/KB/MB (by default the browser reports the size in absolute bytes).
  • Generate a thumbnail preview of the image by calling window.URL.createObjectURL(curFiles[i]) and reducing the image size in the CSS, then insert that image into the list item too.

  function updateImageDisplay() < while(preview.firstChild) < preview.removeChild(preview.firstChild); >var curFiles = input.files; if(curFiles.length === 0) < var para = document.createElement('p'); para.textContent = 'No files currently selected for upload'; preview.appendChild(para); >else < var list = document.createElement('ol'); preview.appendChild(list); for(var i = 0; i < curFiles.length; i++) < var listItem = document.createElement('li'); var para = document.createElement('p'); if(validFileType(curFiles[i])) < para.textContent = 'File name ' + curFiles[i].name + ', file size ' + returnFileSize(curFiles[i].size) + '.'; var image = document.createElement('img'); image.src = window.URL.createObjectURL(curFiles[i]); listItem.appendChild(image); listItem.appendChild(para); >else < para.textContent = 'File name ' + curFiles[i].name + ': Not a valid file type. Update your selection.'; listItem.appendChild(para); >list.appendChild(listItem); > > >

  The custom validFileType() function takes a File object as a parameter, then loops through the list of allowed file types, checking if any matches the file’s type property. If a match is found, the function returns true . If no match is found, it returns false .

  var fileTypes = [ 'image/jpeg', 'image/pjpeg', 'image/png' ] function validFileType(file) < for(var i = 0; i < fileTypes.length; i++) < if(file.type === fileTypes[i]) < return true; >> return false; >

  The returnFileSize() function takes a number (of bytes, taken from the current file’s size property), and turns it into a nicely formatted size in bytes/KB/MB.

  function returnFileSize(number) < if(number < 1024) < return number + 'bytes'; >else if(number > 1024 && number < 1048576) < return (number/1024).toFixed(1) + 'KB'; >else if(number > 1048576) < return (number/1048576).toFixed(1) + 'MB'; >>

  The example looks like this — have a play:

  Specifications

  Specification	Status	Comment
  HTML Living Standard The definition of » in that specification.	Living Standard	Initial definition
  HTML 5.1 The definition of » in that specification.	Recommendation	Initial definition

  Browser compatibility

  Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari
  Basic support	1.0	?	1.0 (1.7 or earlier)	(Yes)	1.0	1.0

  Feature	Android	Chrome for Android	Edge	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	iOS WebKit (Safari/Chrome/Firefox/etc)
  Basic support	(Yes)	(Yes)	(Yes)	4.0 (4.0)	(Yes)	(Yes)	(Yes)

  See also

  Источник