Undefined or null for AngularJS

Question

When I write watch handling functions I check newVal param on undefined and null  Why does AngularJS have such a behavior  but doesn t have particular utility method  So there is angular isUndefined but not angular isUndefinedOrNull  It isn t hard to implement that by hand but how extend angular to have that function in each controller  Tnx   Edit   The example    scope  watch  model   function newVal        if  angular isUndefined newVal     newVal    null  return         do somethings with newVal     Is it common accepted practice to handle such a way   Edit 2   The JSFiddle example  http   jsfiddle net ubA9r      lt div ng-app  App  gt     lt div ng-controller  MainCtrl  gt          lt select ng-model  model  ng-options  m for m in models  gt             lt option value    class  ng-binding  gt Choose model lt  option gt         lt  select gt          model      lt  div gt   lt  div gt   var app   angular module  App         var MainCtrl   function  scope         scope models     Apple    Banana         scope  watch  model   function newVal            console log newVal

User · Answer

I asked the same question of the lodash maintainers a while back and they replied by mentioning the != operator can be used here:

if(newVal != null) {
  // newVal is defined
}

This uses JavaScript's type coercion to check the value for undefined or null.

If you are using JSHint to lint your code, add the following comment blocks to tell it that you know what you are doing - most of the time != is considered bad.

/* jshint -W116 */ 
if(newVal != null) {
/* jshint +W116 */
  // newVal is defined
}

User · Answer

Why not simply use angular isObject with negation  e g   if   angular isObject obj         return

User · Answer

You can always add it exactly for your application   angular isUndefinedOrNull   function val        return angular isUndefined val     val     null

User · Answer

STEVER s answer is satisfactory   However  I thought it may be useful to post a slightly different approach   I use a method called isValue which returns true for all values except null  undefined  NaN  and Infinity   Lumping in NaN with null and undefined is the real benefit of the function for me   Lumping Infinity in with null and undefined is more debatable  but frankly not that interesting for my code because I practically never use Infinity   The following code is inspired by Y Lang isValue   Here is the source for Y Lang isValue          A convenience method for detecting a legitimate non-null value     Returns false for null undefined NaN Infinity  true for other values     including 0 false        method isValue     static     param o The item to test      return  boolean  true if it is not null undefined NaN    false      angular isValue   function val      return   val     null     angular isDefined val      angular isNumber val   amp  amp   isFinite val          Or as part of a factory   factory  lang   function        return                  A convenience method for detecting a legitimate non-null value         Returns false for null undefined NaN Infinity  true for other values         including 0 false            method isValue         static         param o The item to test          return  boolean  true if it is not null undefined NaN    false              isValue  function val          return   val     null     angular isDefined val      angular isNumber val   amp  amp   isFinite val

User · Answer

lodash provides a shorthand method to check if undefined or null    isNil yourVariable

User · Answer

My suggestion to you is to write your own utility service   You can include the service in each controller or create a parent controller  assign the utility service to your scope and then every child controller will inherit this without you having to include it   Example   http   plnkr co edit NI7V9cLkQmEtWO36CPXy p preview  var app   angular module  plunker         app controller  MainCtrl   function  scope  Utils         scope utils   Utils       app controller  ChildCtrl   function  scope  Utils        scope undefined1   Utils isUndefinedOrNull 1       standard DI     scope undefined2    scope utils isUndefinedOrNull 1       MainCtrl is parent       app factory  Utils   function       var service          isUndefinedOrNull  function obj             return  angular isDefined obj     obj   null                 return service        Or you could add it to the rootScope as well   Just a few options for extending angular with your own utility functions

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