How to open a pdf downloaded from an API with JavaScript

On my most recent assignment I was faced with the challenge of downloading a pdf file from an API and displaying it in the browser.

Normally, the API would provide a json-object with a link to the pdf, which can then be used to open a new browser tab/window and the browser or platform takes care of the rest.

In this case however the API was designed for native mobile apps and required the presence of a custom ‘api-key’ http-header, which made it impossible to just provide the url to the browser.

To solve this it was necessary to download the file to memory with an XHR request and then get the browser to open or download it with whatever plugin/UI it normally uses for pdf file.

For the XHR request we use the Fetch API with the whatwg-fetch polyfill. In essence the Fetch API fetch() method returns a response, from which a blob can be created. This blob object can be use to create an objectURL, which can then be used as href in a link.

 

This solution works on Chrome, Safari, Opera, IE11 and Edge.

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