Images downloaded as .part file
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i want to allow user to download some png image in my HTML page.

 i searched and i found this :

`window.location.href = img.src.replace('image/png', 'image/octet-stream');`

it's works fine (open a dialog to save the image file ).

but the problem that the file name looks like : `<random letters>.part`.

so how to solve this ? 

and can i change my own file name ?

thanks in advance.