Comparing angular.isDefined and typeof

Question

Comparing angular.isDefined and typeof

Is there an angular equivalent to the typeof operator in JavaScript that can detect variables not defined? I am specifically interested in the behavior of angular.isDefined() and how it differs from typeof. In the example below, the variable x is not Defined, however, using typeof x does not throw any errors. On the other hand, if we had used angular.isDefined, a "not defined error" would have been thrown.

 if(typeof x != 'undefined')
     alert("defined");
 else 
      alert("undefined");

When using angular.isDefined(x), a

Uncaught ReferenceError: x is not defined

error is thrown if x is not Defined.

  if(angular.isDefined(x)) // throws error because x is not defined
     alert("defined");
 else 
      alert("undefined");

     var x;
      if(angular.isDefined(x)) // does not throw error as x is defined though not **initialiased** 
         alert("defined");
      else 
         alert("undefined");

Is there an Angular solution similar to typeof x != 'undefined'? I am facing this situation where I cannot modify the createContext() function which defines context = "something useful". There are two controllers involved - commonController and contextController. The commonController registers for a custom event handler that requires access to context, but sometimes this event handler is triggered before createContext() is called. Moving createContext() outside of contextController is not an option. How can I handle this scenario in Angular?

javascript angularjs

Answer 1

Answer №1

After further discussion in the comments on @squiroid's response, it appears that your canvasDesign function is structured like this:

canvasDesign = function() { 
    var canvas1 = document.getElementById("canvas1"); 
    if(canvas1 != null) context1 = canvas1.getContext('2d');
}

This function is unintentionally creating an implicit global variable (due to the absence of var before context1).

Using implicit globals is considered a risky practice, especially with ES5 strict mode regulations in place. It is important to rectify such coding habits to avoid potential issues. If modifying the code is not feasible, you can still use typeof context1 === 'undefined'. As discussed in this thread, creating a universal function for variable existence checks proves challenging.

Alternatively, consider these two suggestions:

Employ
```
angular.isDefined(window.context1)
```
to ascertain the presence of a global variable without triggering errors. However, be aware that this method may fail if the variable transitions to a non-global scope at any point.
Declare var context1; at the beginning of your script, outside all functions. By preemptively declaring the variable, you ensure its existence and safety when using angular.isDefined(context1).

Answer 2

After further discussion in the comments on @squiroid's response, it appears that your canvasDesign function is structured like this:

canvasDesign = function() { 
    var canvas1 = document.getElementById("canvas1"); 
    if(canvas1 != null) context1 = canvas1.getContext('2d');
}

This function is unintentionally creating an implicit global variable (due to the absence of var before context1).

Using implicit globals is considered a risky practice, especially with ES5 strict mode regulations in place. It is important to rectify such coding habits to avoid potential issues. If modifying the code is not feasible, you can still use typeof context1 === 'undefined'. As discussed in this thread, creating a universal function for variable existence checks proves challenging.

Alternatively, consider these two suggestions:

Employ
```
angular.isDefined(window.context1)
```
to ascertain the presence of a global variable without triggering errors. However, be aware that this method may fail if the variable transitions to a non-global scope at any point.
Declare var context1; at the beginning of your script, outside all functions. By preemptively declaring the variable, you ensure its existence and safety when using angular.isDefined(context1).

Answer 3

Answer №2

When it comes to checking if an object is defined, angular.isDefined(obj) may not always be a perfect replacement for typeof.

The definition of isDefined can be found on this documentation page:

function isDefined(value) {return typeof value !== 'undefined';}

It is evident that this function essentially uses typeof on the backend, but with the addition of strict type checking using !== instead of !=.

Therefore, in some cases, you may find that typeof works while angular.isDefined() does not provide the desired outcome.

Keep in mind that depending on your specific requirements, you can choose to utilize either typeof or angular.isDefined().

Answer 4

When it comes to checking if an object is defined, angular.isDefined(obj) may not always be a perfect replacement for typeof.

The definition of isDefined can be found on this documentation page:

function isDefined(value) {return typeof value !== 'undefined';}

It is evident that this function essentially uses typeof on the backend, but with the addition of strict type checking using !== instead of !=.

Therefore, in some cases, you may find that typeof works while angular.isDefined() does not provide the desired outcome.

Keep in mind that depending on your specific requirements, you can choose to utilize either typeof or angular.isDefined().

Answer 5

Answer №3

The question about finding an angular alternative to typeof x !='undefined' may be confusing.

In JavaScript, regardless of Angular, it is incorrect to use an undeclared variable like this:

function bar(y) { return true; }
bar(z); // triggers "Uncaught ReferenceError: z is not defined"

Even in Angular, the isDefined function will throw an error when called with an undefined variable.

Answer 6

The question about finding an angular alternative to typeof x !='undefined' may be confusing.

In JavaScript, regardless of Angular, it is incorrect to use an undeclared variable like this:

function bar(y) { return true; }
bar(z); // triggers "Uncaught ReferenceError: z is not defined"

Even in Angular, the isDefined function will throw an error when called with an undefined variable.

Comparing angular.isDefined and typeof

Answer №1

Answer №2

Answer №3

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