CODEWITHSUNDEEP
angularjs
zoomZoom
zoomZoom

Reputation: 339

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

I've tried:

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

and 

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

Upvotes: 6

Views: 1940

Answers (2)

john Smith
john Smith

Reputation: 17906

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

Upvotes: 2

rmuller
rmuller

Reputation: 1837

! is the logical not operator in JavaScript while angular.isUndefined(value) checks if the reference is undefined

Which one to use completely depends on what you are trying to do in the end.

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators and https://docs.angularjs.org/api/ng/function/angular.isUndefined

Upvotes: 0

Related Questions