A href download downloads browser memory

It is one thing to obtain a blob object and another thing altogether to work with it. One thing you want to be able to do is to read the content of the blob. That sounds like a good opportunity to use a FileReader object. You can learn about FileReader objects here. A FileReader object provides some very helpful methods for asynchronously reading the content of blob objects or files in different ways. The FileReader interface has pretty good browser support and supports reading blob data as follows as at the time of this writing :.

Here is what a typical object URL looks like:. The URL. Here is what it looks like:. It is important to note that, this method will always return a new object URL each time it is called, even if it is called with the same blob object. Whenever an object URL is created, it stays around for the lifetime of the document on which it was created. Usually, the browser will release all object URLs when the document is being unloaded. However, it is important that you release object URLs whenever they are no longer needed in order to improve performance and minimize memory usage.

It takes the object URL to be released as its argument. For example:. We have also seen how we can programmatically extract or generate content in the browser using Web APIs. In this section, we will examine how we can download programmatically generate content in the browser, leveraging all we have learned from the beginning of the article and what we already know about blobs and object URLs.

The logic of our helper function can be broken down as follows:. Here is what an implementation of this helper function will look like:. That was a pretty straightforward implementation of the download link helper function. Notice that the helper triggers a one-off automatic download of the blob content whenever it is called. Also notice that the helper function takes a filename as its second argument, which is very useful for setting the default filename for the downloaded file.

Now that we have our download helper function in place, we can revisit our previous examples and modify them to trigger a download for the generated content.

Here we go. We will update the final promise. Here we have updated the final promise. Here is a working and more advanced example of this application on Codepen :. We will add some code to the end of the load event listener of the img object, to allow us:. Here is a working example of this application on Codepen :. Get certified by completing a course today! If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:.

Example Specify a value for the download attribute, which will be the new filename of the downloaded file "w3logo. Report Error. Your message has been sent to W3Schools. Microsoft Edge Never forget a password thanks to this impressive password management tool. Moon Invoice - Easy Invoicing 6. A cross-platform invoicing and billing app suitable for a range of jobs and industries.

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