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want to check null values. any() method returns null or array of matched result (actually there's a match() method inside which is returned). 

$scope.isMobileBrowser = !isMobile.any() ? false : true;

If any() method returns null I want false to be assigned to $scope.isMobileBrowser variable, otherwise true. will the over mentioned snippet fail in any probable case? Is there any other more efficient workaround?

for more details of isMobile object:

var isMobile = {
    Android: function() {
        return navigator.userAgent.match(/Android/i);
    },
    BlackBerry: function() {
        return navigator.userAgent.match(/BlackBerry/i);
    },
    iOS: function() {
        return navigator.userAgent.match(/iPhone|iPad|iPod/i);
    },
    Opera: function() {
        return navigator.userAgent.match(/Opera Mini/i);
    },
    Windows: function() {
        return navigator.userAgent.match(/IEMobile/i);
    },
    any: function() {
        return (isMobile.Android() || isMobile.BlackBerry() || isMobile.iOS() || isMobile.Opera() || isMobile.Windows());
    }
};
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5
  • Is there any other more efficient workaround? - Are you sure that your program is slow just because of this line? Commented Oct 8, 2015 at 6:35
  • No, it's not slow. I would like to know the correctness, also if there exists any other better options. Commented Oct 8, 2015 at 6:36
  • 1
    If you really don't need the returned array, use test() instead of match(). Commented Oct 8, 2015 at 6:38
  • 1
    String.match does not return a string. It returns null or Array. Commented Oct 8, 2015 at 6:57
  • Please add the any method as well too check what values will be returned. Commented Oct 8, 2015 at 7:10

4 Answers 4

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5

Empty string is also a falsy value.
If any() returns an empty string, !isMobile.any() ? false : true will return false, but you probably want true.

This means your code is incorrect for this case.

I'd just do something like isMobile.any() !== null.

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2 Comments

Why would any return an empty string? As @Salman commented in the original Question?
@sabithpocker The OP states any() method returns null or string. That's the only thing for sure. The additional "actually there's a match() method inside which is returned" suggests some implementation details, but quite vague. @Salman's also suggests that there's more going on there. So with the question as it is formulated now, we have null or string returned and there's nothing prohibiting this string to be empty.
1

As per the any() function, you are returning value of the following expression:

(isMobile.Android() || isMobile.BlackBerry() || isMobile.iOS() 
                             || isMobile.Opera() || isMobile.Windows())

Each of these functions can either return an Array or null as seen in the doc for match

So while evaluating the OR it will evaluate to the first truth value encountered and doesnt evaluate any further as the expression is already fit to be true. So, for example if the browser is android the expression evaluates to ["Android"]. If windows it will be ["Windows"]. If none of these, it will be null. Which makes it clear that any() can only return an Array or null.

isMobileBrowser should be true if it's any of these mobile browsers, which means isMobileBrowser should be true if:

any() evaluates to an Array

OR in other way:

If any() does not evaluate to null

which is:

$scope.isMobileBrowser = isMobile.any() instanceof Array;//looks messy
$scope.isMobileBrowser = (isMobile.any()).constructor === Array;//looks messy
$scope.isMobileBrowser = Array.isArray(isMobile.any());//looks messy
$scope.isMobileBrowser = Object.prototype.toString.call(isMobile.any()) 
                                   === "[object Array]";//looks messy

OR the other way:

$scope.isMobileBrowser = isMobile.any() !== null;
$scope.isMobileBrowser = !(isMobile.any() === null);
isMobileBrowser = !(Object.prototype.toString.call(isMobile.any()) 
                                   === "[object Null]");//looks messy

So we just discussed different ways to check for null and Array. You have two possible sets of outputs

  1. null value which is always false
  2. An Array which is always true (You can check this empty array scenario although that doesn't apply here)

So you can simply do the following to convert those to exact boolean without worrying much:

isMobileBrowser = Boolean(isMobile.any()); //to convert value to boolean
isMobileBrowser = !!isMobile.any(); //another way to convert to boolean
                                   //!!["Android"] is true
                                   //!!null is false

@rossipedia explains the !! well in his answer.

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0

A compact way of representing what you want would be:

$scope.isMobileBrowser = !!isMobile.any();

The !! there does two things:

  1. The first ! evaluates the "truthiness"1 of the return value of isMobile.any() and then negates it.
  2. The second ! negates that value again.

So what you end up with is false if .any() returns null, otherwise true.

However, this may fail in edge cases where .any() returns something that is "falsy". In that case, checking for null specifically is what you want:

isMobile.any() !== null

1: "Truthiness":

In JavaScript, a truthy value is a value that translates to true when evaluated in a Boolean context. All values are truthy unless they are defined as falsy (i.e., except for false, 0, "", null, undefined, and NaN).

From MDN

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1 Comment

!!isMobile.any() will be false if any() returns "". Should be true according to the question.
-1

Try this:

$scope.isMobileBrowser = isMobile.any() === null;

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2 Comments

I think === is wrong: If any() method returns null I want false to be assigned to $scope.isMobileBrowser variable...
Please consider editing your post to add more explanation about what your code does and why it will solve the problem. An answer that mostly just contains code (even if it's working) usually wont help the OP to understand their problem. It's also recommended that you don't post an answer if it's just a guess. A good answer will have a plausible reason for why it could solve the OP's issue.

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