Form Helpers — Ruby on Rails Guides

Form Helpers — Ruby on Rails Guides: "5.2 Dealing with Ajax
Unlike other forms making an asynchronous file upload form is not as simple as providing form_for with remote: true. With an Ajax form the serialization is done by JavaScript running inside the browser and since JavaScript cannot read files from your hard drive the file cannot be uploaded. The most common workaround is to use an invisible iframe that serves as the target for the form submission."



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