To set the value of a Boolean attribute, such as disabled, you can specify any value. An empty string or the name of the attribute are recommended values. All that matters is that if the attribute is present at all, regardless of its actual value, its value is considered to be true. The absence of the attribute means its value is false. By setting the value of the disabled attribute to the empty string (""), we are setting disabled to true, which results in the button being disabled.
var f = document.querySelectorAll( "label.disabled input" );
for( var i = 0; i < f.length; i++ )
{
// Reference
var e = f[ i ];
// Actions
e.setAttribute( "disabled", false|null|undefined|""|0|"disabled" );
/*
<input disabled="false"|"null"|"undefined"|empty|"0"|"disabled">
e.getAttribute( "disabled" ) === "false"|"null"|"undefined"|""|"0"|"disabled"
e.disabled === true
*/
e.removeAttribute( "disabled" );
/*
<input>
e.getAttribute( "disabled" ) === null
e.disabled === false
*/
e.disabled = false|null|undefined|""|0;
/*
<input>
e.getAttribute( "disabled" ) === null|null|null|null|null
e.disabled === false
*/
e.disabled = true|" "|"disabled"|1;
/*
<input disabled>
e.getAttribute( "disabled" ) === ""|""|""|""
e.disabled === true
*/
}