<input> элемент с атрибутомtype="file" позволяет пользователю выбрать один файл или более из файлового хранилища своего устройства. После выбора эти файлы могут быть загружены на сервер при помощиформы, или обработаны JavaScript иFile API.

Интерактивный пример

<label for="avatar">Choose a profile picture:</label><input type="file" name="avatar" accept="image/png, image/jpeg" />

label {  display: block;  font:    1rem "Fira Sans",    sans-serif;}input,label {  margin: 0.4rem 0;}

Значение

Атрибутvalue элементаinput содержит строку, представляющую путь к выбранному файлу или файлам. Если пользователь выбрал несколько файлов,value представляет первый файл из списка. Остальные файлы можно определить используясвойствоHTMLInputElement.files элементаinput.

Additional attributes

In addition to the common attributes shared by all<input> elements, inputs of typefile also support:

files

AFileList object that lists every selected file. This list has no more than one member unless themultiple attribute is specified.

Using file inputs

A basic example

<form method="post" enctype="multipart/form-data">  <div>    <label for="file">Choose file to upload</label>    <input type="file" name="file" multiple />  </div>  <div>    <button>Submit</button>  </div></form>

div {  margin-bottom: 10px;}

This produces the following output:

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 themultiple 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 downShift orControl, and then clicking). If you only want the user to choose a single file per<input>, omit themultiple 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'sHTMLInputElement.files property, which is aFileList object containing a list ofFile objects. TheFileList behaves like an array, so you can check itslength property to get the number of selected files.

EachFile object contains the following information:

name

The file's name.

lastModified

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).

lastModifiedDateУстарело

ADate object representing the date and time at which the file was last modified.This is deprecated and should not be used. UselastModified instead.

size

The size of the file in bytes.

type

The file'sMIME type.

webkitRelativePathНе стандартно

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

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 asJPEG orPNG.

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

• accept="image/png" oraccept=".png" — Accepts PNG files.
• accept="image/png, image/jpeg" oraccept=".png, .jpg, .jpeg" — Accept PNG or JPEG files.
• accept="image/*" — Accept any file with animage/* 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 upload</label>    <input      type="file"           name="profile_pic"      accept=".jpg, .jpeg, .png" />  </div>  <div>    <button>Submit</button>  </div></form>

div {  margin-bottom: 10px;}

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

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 theaccept value (the exact nature differs across browsers and operating systems).

Theaccept 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 theaccept 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 theHTMLInputElement.files property, as well as showing off a few clever tricks.

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"           name="image_uploads"      accept=".jpg, .jpeg, .png"      multiple />  </div>  <div>    <p>No files currently selected for upload</p>  </div>  <div>    <button>Submit</button>  </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.

In the first lines of script, we get references to the form input itself, and the<div> element with the class of.preview. Next, we hide the<input> element — we do this because file inputs tend to be ugly, difficult to style, and inconsistent in their design across browsers. You can activate the input element by clicking its<label>, so it is better to visually hide the input and style the label like a button, so the user will know to interact with it if they want to upload files.

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

Next, we add anevent 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 customupdateImageDisplay() function.

input.addEventListener("change", updateImageDisplay);

Whenever theupdateImageDisplay() function is invoked, we:

• Use awhile loop to empty the previous contents of the preview<div>.

• Grab theFileList object that contains the information on all the selected files, and store it in a variable calledcurFiles.

• Check to see if no files were selected, by checking ifcurFiles.length is equal to 0. If so, print a message into the preview<div> stating that no files have been selected.

• If fileshave been selected, we loop through each one, printing information about it into the preview<div>. Things to note here:

• We use the customvalidFileType() function to check whether the file is of the correct type (e.g. the image types specified in theaccept attribute).

• If it is, we:

  • Print out its name and file size into a list item inside the previous<div> (obtained fromcurFiles[i].name andcurFiles[i].size). The customreturnFileSize() 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 callingwindow.URL.createObjectURL(curFiles[i]) and reducing the image size in the CSS, then insert that image into the list item too.

• If the file type is invalid, we display a message inside a list item telling the user that they need to select a different file type.

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 customvalidFileType() function takes aFile object as a parameter, then loops through the list of allowed file types, checking if any matches the file'stype property. If a match is found, the function returnstrue. If no match is found, it returnsfalse.

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;}

ThereturnFileSize() function takes a number (of bytes, taken from the current file'ssize 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:

Техническое резюме

Спецификации

Совместимость с браузерами

Смотрите также

• Using files from web applications — contains a number of other useful examples related to<input type="file"> and theFile API.