what is the difference between angular.isUndefined(value) and not !(value)?

Question

I've tried:

if(angular.isUndefined(value)){
    // something
}

and

if(!(value)){
    // something
}

• Is there a difference between the two?
• Is there a use-case to choose one instead of the other?

Answer 1

var foo = false; 


if(!foo) {
  // will log
  console.log("foo is defined but false");
}

if(angular.isUndefined(foo)){
   // will not log as foo is defined
   console.log("foo is undefined")
}

another example without define foo

if(!foo) {
  // will throw exception "Uncaught ReferenceError: foo is not defined "
  console.log("foo is defined but false");
}

if(angular.isUndefined(foo)){
   // will log
   console.log("foo is undefined")
}

so effective angular.isUndefined(foo) does nothing else than evaluating

if(typeof foo == "undefined")

wrapped for saving 1 character yeah.

while !-operator checks if a defined variable evaluates to false so

if(!foo) 

is the same like

if( foo != true)

UPDATE:

As stated in comments, when i write "evaluates to false" there is false null undefined NaN ""(empty string) and 0 included