**Strict answer**: Because the JS spec [says so](http://es5.github.io/#x11.9.6):

  &gt; - If Type(x) is Number, then
 &gt;   - If x is NaN, return false.
 &gt;   - If y is NaN, return false.

----

**Useful answer**: The IEEE 754 spec for floating-point numbers (which is used by all languages for floating-point) says that NaNs are never equal.

This behaviour is specified by the [IEEE-754 standard][1] (which the JavaScript spec follows in this respect).

For an extended discussion, see https://stackoverflow.com/questions/1565164/what-is-the-rationale-for-all-comparisons-returning-false-for-ieee754-nan-values


  [1]: http://en.wikipedia.org/wiki/IEEE_floating_point

Although either side of `NaN===NaN` contains the same value and their type is `Number` but they are not same. According to ECMA-262, either side of `==` or `===` contains `NaN` then it will result false value.

you may find a details rules in here-

http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3

I&#39;ve just discovered `git checkout --orphan`, but I don&#39;t know how to use it. Its help page says it creates a **new unparented branch**. 

In the `master` branch, I&#39;ve tried `git checkout --orphan br`, only to see the files in the working directory change to &amp;ldquo;Changes to be committed&amp;rdquo;, and the `git log` saying `fatal: bad default revision &#39;HEAD&#39;`.

So what&#39;s the advantage of using  `git checkout --orphan`?

What is `git checkout --orphan` used for?

I&#39;m using the default navbar and a couple of the list items are dropdowns. I&#39;m not able to click the link that triggers the dropdown. I know that I could just add a duplicate link into the dropdown but I&#39;d rather not. Is it possible to make the head link a clickable link (not just a handle for the dropdown)?

For reference, see the first link in the dropdown below. I want users to be able to click it and actually go to the page it points to.

&lt;!-- language: lang-html --&gt;

    &lt;nav class=&quot;navbar navbar-fixed-top admin-menu&quot; role=&quot;navigation&quot;&gt;
      &lt;div class=&quot;navbar-header&quot;&gt;...&lt;/div&gt;
       &lt;!-- Collect the nav links, forms, and other content for toggling --&gt;
       &lt;div class=&quot;collapse navbar-collapse&quot; id=&quot;bs-example-navbar-collapse-1&quot;&gt;
         &lt;ul class=&quot;nav navbar-nav navbar-right&quot;&gt;
           &lt;li class=&quot;dropdown&quot;&gt;
             &lt;a class=&quot;dropdown-toggle&quot; data-toggle=&quot;dropdown&quot; href=&quot;#&quot;&gt;
               I DONT WORK! &lt;b class=&quot;caret&quot;&gt;&lt;/b&gt;
             &lt;/a&gt;
             &lt;ul class=&quot;dropdown-menu&quot;&gt;
               &lt;li&gt;&lt;a href=&quot;/page2&quot;&gt;Page2&lt;/a&gt;&lt;/li&gt;
             &lt;/ul&gt;
           &lt;/li&gt;
           &lt;li&gt;&lt;a href=&quot;#&quot;&gt;I DO WORK&lt;/a&gt;&lt;/li&gt;
         &lt;/ul&gt;				 
       &lt;/div&gt;&lt;!-- /.navbar-collapse --&gt;
     &lt;/nav&gt;


Bootstrap 3: how to make head of dropdown link clickable in navbar

Why does `NaN === NaN` return `false`  in Javascript?

    &gt; undefined === undefined
    true
    &gt; NaN === NaN
    false
    &gt; a = NaN
    NaN
    &gt; a === a
    false

On the [documentation page](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN) I see this:

&gt;## Testing against NaN
&gt;
&gt;Equality operator (`==` and `===`) cannot be used to test a value against `NaN`. Use `isNaN` instead.

Is there any reference that answers to the question? It would be welcome.


Why is NaN === NaN false?

Why does <code>NaN === NaN</code> return <code>false</code> in Javascript?
<pre><code class="hljs language-ini">> undefined === undefined
true
> NaN === NaN
false
> a = NaN
NaN
> a === a
false
</code></pre>
On the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN" target="_blank" rel="noopener noreferrer">documentation page</a> I see this:
>## Testing against NaN
>
>Equality operator (<code>==</code> and <code>===</code>) cannot be used to test a value against <code>NaN</code>. Use <code>isNaN</code> instead.
Is there any reference that answers to the question? It would be welcome.

We all know that 0&lt;sup&gt;0&lt;/sup&gt; is indeterminate.

**But**, *javascript* says that:

    Math.pow(0, 0) === 1 // true

and *C++* says the same thing:

    pow(0, 0) == 1 // true

WHY?

I know that:

    &gt;Math.pow(0.001, 0.001)
    0.9931160484209338

But why does `Math.pow(0, 0)` throw no errors? Or maybe a `NaN` would be better than `1`.

Why is Math.pow(0, 0) === 1?

I am looking for an efficient way to remove all elements from a javascript array if they are present in another array.

    // If I have this array:
    var myArray = [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;, &#39;e&#39;, &#39;f&#39;, &#39;g&#39;];

    // and this one:
    var toRemove = [&#39;b&#39;, &#39;c&#39;, &#39;g&#39;];


I want to operate on myArray to leave it in this state: `[&#39;a&#39;, &#39;d&#39;, &#39;e&#39;, &#39;f&#39;]`

With jQuery, I&#39;m using `grep()` and `inArray()`, which works well:

    myArray = $.grep(myArray, function(value) {
        return $.inArray(value, toRemove) &lt; 0;
    });


Is there a pure javascript way to do this without looping and splicing?

    
    


Remove all elements contained in another array

I need to send a GET request using the `$http` service. One of the parameters will be an array of ids. The url looks like this one **mysite.com/items?id[]=1&amp;id[]=2&amp;id[]=3&amp;id[]=4**

I tried this approach

&lt;!-- language: lang-js --&gt;
    
    $http(
      method: &#39;GET&#39;,
      url: &#39;/items&#39;,
      params: {
        id: ids // ids is [1, 2, 3, 4]
      }
    )

but the url I obain is **mysite.com/items?id=%5B%221%22%2C%222%22%2C%223%22%2C%224%22%5D**

That&#39;s Because Angular is converting my value in a JSON string. Is there a way to get the behavior I want?

**[Update]**

I solved the issue thanks to Jonathan&#39;s suggestion using jQuery&#39;s `$.param()`.

&lt;!-- language: lang-js --&gt;

    $http(
      method: &#39;GET&#39;
      url: &#39;/items?&#39; + $.param({id: ids})
    )

Send array via GET request with AngularJS&#39; $http service

In the [Lodash][1] library, can someone provide a better explanation of [merge](http://lodash.com/docs#merge) and [extend / assign][2].  

Its a simple question but the answer evades me nonetheless. 

  [1]: http://www.lodash.com
  [2]: http://lodash.com/docs#assign

Lodash - difference between .extend() / .assign() and .merge()

Using `&lt;input type=number&gt;` will cause `this.value` inside of an event listener to return an empty string if the input is not a valid number.  You can see an example of this at http://jsfiddle.net/fSy53/

However, the invalid characters are still displayed in the input.

Is there any way to get the value that is actually *displayed*, including the invalid characters, from within an event listener?

My ultimate goal is to prevent users from actually typing any non-numeric characters into the field.  I need to use `type=number` so that the numeric virtual keyboard is used by mobile devices.  My goal would be to do something like `this.value = this.value.replace(/[^0-9.]/g, &quot;&quot;)` on `keyup keypress`, but this doesn&#39;t work because if an invalid character is typed, reading from `this.value` returns `&quot;&quot;`.

Prevent typing non-numeric in input type number

While the first part of the question (which is in the title) has been answered a few times before (i.e., https://stackoverflow.com/questions/10034149/why-is-nan-not-equal-to-nan), I don&#39;t see why the second piece works the way it does (inspired by this question https://stackoverflow.com/questions/20319813/how-to-check-list-containing-nan#comment30324111_20319813)?

Namely:

    &gt;&gt; nan == nan
    False

    &gt;&gt; nan in [nan]
    True

______

An explanatory addendum to the question considering the answer from @DSM. So, why `float(&quot;nan&quot;)` is behaving differently from `nan`? Shouldn&#39;t it evaluate again to simple `nan` and why interpreter behaves this way?

    &gt;&gt; x = float(&quot;nan&quot;)
    &gt;&gt; y = nan
    &gt;&gt; x
    nan
    &gt;&gt; y
    nan
    &gt;&gt; x is nan, x is float(&quot;nan&quot;), y is nan
    (False, False, True)

Basically, it refers to same generic `nan` in the first case, but creates separate object in the second:

    &gt;&gt; nans = [nan for i in range(2)]
    &gt;&gt; map(id, nans)
    [190459300, 190459300]
    &gt;&gt; nans = [float(&quot;nan&quot;) for i in range(2)]
    &gt;&gt; map(id, nans)
    [190459300, 190459301]

Why in numpy `nan == nan` is False while nan in [nan] is True?

Is there any modern browser that raises exceptions on NaN propagation (ie multiplying or adding a number to NaN), or that can be configured to do so?

Silent NaN propagation is an awful and insidious source of bugs, and I&#39;d love to be able to detect them early, even at a performance penalty.

---

Here&#39;s an example bug that `use strict`, `jshint` et al. wouldn&#39;t pick up:

    object = new MyObject();
    object.position.x = 0;
    object.position.y = 10;

    // ... lots of code

    var newPosition = object.position + 1; // &lt;- this is an error, and should
                                           //    have been object.position.x
                                           //    however it fails *silently*,
                                           //    rather than loudly

    newPosition *= 2;                      // &lt;- this doesn&#39;t raise any errors either.
                                           //    this code is actually ok if the
                                           //    previous line had been correct

---

Note: The TypeScript compiler is able to detect errors like the above, even in JS code, if type inference succeeds.

Break on NaN in JavaScript

I need to calculate the number of non-NaN elements in a numpy ndarray matrix. How would one efficiently do this in Python? Here is my simple code for achieving this: 

    import numpy as np

    def numberOfNonNans(data):
        count = 0
        for i in data:
            if not np.isnan(i):
                count += 1
        return count 

Is there a built-in function for this in numpy? Efficiency is important because I&#39;m doing Big Data analysis. 

Thnx for any help! 

Counting the number of non-NaN elements in a numpy ndarray in Python

I have table `x`:

            website
    0 	http://www.google.com/
    1 	http://www.yahoo.com
    2 	None

I want to replace python None with pandas NaN. I tried:

    x.replace(to_replace=None, value=np.nan)

But I got:

    TypeError: &#39;regex&#39; must be a string or a compiled regular expression or a list or dict of strings or regular expressions, you passed a &#39;bool&#39;

How should I go about it? 
 


Replace None with NaN in pandas dataframe

Which is the equivalent of `isnan()` in Swift ? 
I need to check if some operation results are valid and delete those invalid like x/0
Thanks

Content Type	Original Author	Original Content on Stackoverflow
Question	Ionică Bizău	View Question on Stackoverflow
Solution 1 - Javascript	SLaks	View Answer on Stackoverflow
Solution 2 - Javascript	NPE	View Answer on Stackoverflow
Solution 3 - Javascript	Md Mehedi Hasan	View Answer on Stackoverflow

Why is NaN === NaN false?

Javascript Problem Overview

Javascript Solutions

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Bootstrap 3: how to make head of dropdown link clickable in navbar

What is `git checkout --orphan` used for?

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