check null,empty or undefined angularjs

Question

I am creating a project using angularjs.I have variable like

$scope.test = null
$scope.test = undefined
$scope.test = \"\"

I want to check all

Answer 1

just use -

if(!a) // if a is negative,undefined,null,empty value then...
{
    // do whatever
}
else {
    // do whatever
}

this works because of the == difference from === in javascript, which converts some values to "equal" values in other types to check for equality, as opposed for === which simply checks if the values equal. so basically the == operator know to convert the "", null, undefined to a false value. which is exactly what you need.