The following input elements are all disabled:

<input disabled />

<input disabled= />

<input disabled=disabled />

<input disabled=true />

<input disabled=false /> <!-- still disabled! -->

If a boolean attribute is present, it's on; otherwise, it's off. The value doesn't mean anything.

However, when dealing with these elements through javascript, you should make use of the corresponding property, i.e.:

myInput.disabled = true; // adds the attribute and disables control

myInput.disabled = false; // removes the attribute and enables control

The property will update the attribute for you. This is true of all boolean attribute / property pairs, i.e.: readonly, checked, selected, etc.

Confusion may stem from the fact that setAttribute() asks for both a name and value and emits markup in a key=value format -even when you don't want a value. When adding a custom boolean attribute, I simply set the attribute without a value (sample):

input.setAttributeNode(document.createAttribute(data-custom));

console.log(input); // <input data-custom>

_{See document.createAttribute() and Element.setAttributeNode().}