Uncaught SyntaxError: Unexpected token else
This is because you haven't used {}
syntax in your if statement. Not using them is fine, but only when you have one line to execute. In this case, your else is the second line and is breaking the "only one line without curly brackets" rule.
Use curly brackets:
if(isChecked) {
console.log("True");
$('#register').removeAttr("disabled");
} else
console.log("False");