How to Download Files via POST with JSON Data in JavaScript/jQuery?

Downloading Files via POST with JSON Data in JavaScript/jQuery

When dealing with RESTful web services, handling both JSON and downloadable binary responses in the client-side is a common challenge. This article addresses how to accomplish this using JavaScript and jQuery.

The desired scenario involves submitting a POST request with JSON data to a REST endpoint. Depending on the request parameters, the response can be either JSON data or a downloadable file. To handle this, we explore several options:

Using AJAX:

The first approach is to use the jQuery $.ajax() function. However, the dataType option for AJAX requests only supports specific data types, including JSON. This means that directly downloading a file using AJAX is not possible.

Generating a File URL on the Server:

An alternative approach is to have the server generate the downloadable file and return a JSON response containing a URL to the file. The client can then use this URL to initiate the download. This method requires multiple server calls, which may not be ideal.

Using an iFrame:

A more optimal solution is to use an iFrame. After submitting the POST request, an iFrame can be created in the client app's body and its src attribute can be set to the provided URL. As the iFrame loads, the browser will prompt the user to download the file.

<code class="javascript">$.post('/create_binary_file.php', postData, function(retData) {
  $("body").append("<iframe src='" + retData.url+ "' style='display: none;' ></iframe>");
});</code>

Advantages of iFrame Method:

• Simplifies the server-side implementation, eliminating the need for file management.
• Allows for the retrieval of additional information (e.g., file size, generation time) before initiating the download.
• Compatible with both JSON and binary file responses.

Considerations:

• This method requires the server to provide a download URL in the JSON response.
• The file URL should be ephemeral to prevent malicious use.
• Browser compatibility may vary, and the display: none style can sometimes result in issues.

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