downloads.download() 编辑

The download() function of the downloads API downloads a file, given its URL and other optional preferences.

• If the specified url uses the HTTP or HTTPS protocol, then the request will include all cookies currently set for its hostname.
• If both filename and saveAs are specified, then the Save As dialog will be displayed, pre-populated with the specified filename.

This is an asynchronous function that returns a Promise.

Syntax

var downloading = browser.downloads.download(
  options                   // object
)

Parameters

options

An object specifying what file you wish to download, and any other preferences you wish to set concerning the download. It can contain the following properties:

allowHttpErrorsOptional

A boolean flag that enables downloads to continue even if they encounter HTTP errors. Using this flag, for example, enables the download of server error pages. Default value false. When set to:

• false, the download is canceled when it encounters an HTTP error.
• true, the download continues when an HTTP error is encountered and the HTTP server error is not reported. However, if the download fails due to file-related, network-related, user-related, or other error, that error is reported.  

bodyOptional

A string representing the post body of the request.

conflictActionOptional

A string representing the action you want taken if there is a filename conflict, as defined in the downloads.FilenameConflictAction type (defaults to "uniquify" when it is not specified).

filenameOptional

A string representing a file path relative to the default downloads directory — this provides the location where you want the file to be saved, and what filename you want to use. Absolute paths, empty paths, path components that start and/or end with a dot (.), and paths containing back-references (../) will cause an error. If omitted, this value will default to the filename already given to the download file, and a location immediately inside the downloads directory.

headersOptional

If the URL uses the HTTP or HTTPS protocols, an array of objects representing additional HTTP headers to send with the request. Each header is represented as a dictionary object containing the keys name and either value or binaryValue. The headers that are forbidden by XMLHttpRequest and fetch cannot be specified, however, Firefox 70 and later enables the use of the Referer header. Attempting to use a forbidden header throws an error.

incognitoOptional

A boolean: if present and set to true, then associate this download with a private browsing session. This means that it will only appear in the download manager for any private windows that are currently open.

methodOptional

A string representing the HTTP method to use if the url uses the HTTP[S] protocol. This may be either "GET" or "POST".

saveAsOptional

A boolean that specifies whether to provide a file chooser dialog to allow the user to select a filename (true), or not (false).

If this option is omitted, the browser will show the file chooser or not based on the general user preference for this behavior (in Firefox this preference is labeled "Always ask you where to save files" in about:preferences, or browser.download.useDownloadDir in about:config).

Note: Firefox for Android raises an error if saveAs is set to true. The parameter is ignored when saveAs is false or not included.

url

A string representing the URL to download.

Return value

A Promise. If the download started successfully, the promise will be fulfilled with the id of the new downloads.DownloadItem. Otherwise, the promise will be rejected with an error message taken from downloads.InterruptReason.

If you use URL.createObjectURL() to download data created in JavaScript and you want to revoke the object URL (with revokeObjectURL) later (as it is strongly recommended), you need to do that after the download has been completed. To do so, listen to the downloads.onChanged event.

Browser compatibility

BCD tables only load in the browser

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Examples

The following snippet attempts to download an example file, also specifying a filename and location to save it in, and the uniquify conflictAction option.

function onStartedDownload(id) {
  console.log(`Started downloading: ${id}`);
}

function onFailed(error) {
  console.log(`Download failed: ${error}`);
}

var downloadUrl = "https://example.org/image.png";

var downloading = browser.downloads.download({
  url : downloadUrl,
  filename : 'my-image-again.png',
  conflictAction : 'uniquify'
});

downloading.then(onStartedDownload, onFailed);

This API is based on Chromium's chrome.downloads API.

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