Html выбрать несколько файлов

Html выбрать несколько файлов

Атрибут value элемента input содержит DOMString , который представляет путь к выбранным файлам. Если пользователь выбрал несколько файлов, value представляет первый файл из списка. Остальные файлы можно определить используя HTMLInputElement.files (en-US) свойство элемента input.

**Примечание:**1. Если выбрано несколько файлов, строка представляет собой первый выбранный файл. JavaScript предоставляет доступ к остальным файлам через свойство FileList . 2. Если не выбрано ни одного файла, .строка равна «» (пустая). 3. Строка начинается с C:\fakepath\ , для предотвращения определения файловой структуры пользователя вредоносным ПО.

Additional attributes

In addition to the common attributes shared by all elements, inputs of type file also support:

A FileList object that lists every selected file. This list has no more than one member unless the multiple attribute is specified.

Using file inputs

A basic example

form method="post" enctype="multipart/form-data"> div> label for="file">Choose file to uploadlabel> input type="file" id="file" name="file" multiple> div> div> button>Submitbutton> div> form> 

This produces the following output:

Примечание: 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 form 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 files property, which is a FileList object containing 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:

A number specifying the date and time at which the file was last modified, in milliseconds since the UNIX epoch (January 1, 1970 at midnight).

A Date object representing the date and time at which the file was last modified. This is deprecated and should not be used. Use lastModified instead.

The size of the file in bytes.

A string specifying the file’s path relative to the base directory selected in a directory picker (that is, a file picker in which the webkitdirectory attribute is set). This is non-standard and should be used with caution.

Примечание: You can set as well as get the value of HTMLInputElement.files in all modern browsers; this was most recently added to Firefox, in version 57 (see баг 1384030).

Limiting accepted file types

Often you won’t want the user to be able to pick any arbitrary type of file; instead, you often want them to select files of a specific type or types. 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 (en-US) .

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:

form method="post" enctype="multipart/form-data"> div> label for="profile_pic">Choose file to uploadlabel> input type="file" id="profile_pic" name="profile_pic" accept=".jpg, .jpeg, .png"> div> div> button>Submitbutton> div> form> 

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

Примечание: 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 simply 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 it possible to override this and select any file they wish, and then choose incorrect file types.

Because of this, you should 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 (en-US) property, as well as showing off a few clever tricks.

Примечание: 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:

form method="post" enctype="multipart/form-data"> div> label for="image_uploads">Choose images to upload (PNG, JPG)label> input type="file" id="image_uploads" name="image_uploads" accept=".jpg, .jpeg, .png" multiple> div> div class="preview"> p>No files currently selected for uploadp> div> div> button>Submitbutton> div> form> 

html  font-family: sans-serif; > form  width: 600px; background: #ccc; margin: 0 auto; padding: 20px; border: 1px solid black; > form ol  padding-left: 0; > form li, div > p  background: #eee; display: flex; justify-content: space-between; margin-bottom: 10px; list-style-type: none; border: 1px solid black; > form img  height: 64px; order: 1; > form p  line-height: 32px; padding-left: 10px; > form label, form button  background-color: #7F9CCB; padding: 5px 10px; border-radius: 5px; border: 1px ridge black; font-size: 0.8rem; height: auto; > form label:hover, form button:hover  background-color: #2D5BA3; color: white; > form label:active, form button:active  background-color: #0D3F8F; color: white; > 

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; 

Примечание: 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 to listen for changes to its selected value changes (in this case, when files are selected). The event listener invokes our custom updateImageDisplay() function.

.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 Определение » в этой спецификации.	Живой стандарт	Initial definition
  HTML 5.1 Определение » в этой спецификации.	Рекомендация	Initial definition

  Browser compatibility

  BCD tables only load in the browser

  See also

  Found a content problem with this page?

  This page was last modified on 17 июл. 2023 г. by MDN contributors.

  Your blueprint for a better internet.

  MDN

  Support

  Our communities

  Developers

  Visit Mozilla Corporation’s not-for-profit parent, the Mozilla Foundation.
  Portions of this content are ©1998– 2023 by individual mozilla.org contributors. Content available under a Creative Commons license.

  Источник

  Читайте также:  Python работа со строками замена символов