HTMLButtonElement: formMethod property

The formMethod property of the HTMLButtonElement interface is the HTTP method used to submit the <form> if the <button> element is the control that submits the form. It reflects the value of the <button>'s formmethod attribute.

The value overrides the method property of the HTMLFormElement interface if the form is submitted via the button. This property can be retrieved or set. If set with an empty or invalid value, the invalid default value is "get". If not set at all, the value is the empty string ("").

btnEl.formMethod = "post";