JavaScript Nan and Infinity Special values [translation]_javascript tips

1.NaN

In JavaScript, Nan represents "not a number". This value is returned primarily when parsing a string error:

Copy Code code as follows:

> Number ("xyz")
Nannan

The name is "not a number", but it can also be said not to a number:

Copy Code code as follows:

> Nan!== nan
True

It's a number! The type is??

Copy Code code as follows:

> typeof NaN
' Number '

1.1 Detection Nan
In JavaScript, Nan is a value that is only one by one and does not want to wait. Therefore, it is not possible to use the Equals operator to determine whether a value is Nan, but there is a global function isNaN () to do it.

Copy Code code as follows:

> isNaN (NaN)
True

Kit Cambridge points to a problem with isNaN () : It implicitly converts its arguments to numbers, so even if the argument is a string that cannot be converted to a number, it returns True (converted to Nan):

Copy Code code as follows:

> Number ("xyz")
NaN
> isNaN ("xyz")
True

For the same reason, isNaN returns true for many other objects as well:

Copy Code code as follows:

> Number ({})
NaN
> isNaN ({})
True

> Number (["Xzy"])
NaN
> isNaN (["Xzy"])
True

The custom object that overridden the ValueOf method also:

Copy Code code as follows:

> var obj = {valueof:function () {return NaN}};
> Number (obj)
NaN
> isNaN (obj)
True

So you can use Nan is the only value that satisfies (x!== x) inequalities to write one's own isNaN function, so that there is no problem mentioned above:

Copy Code code as follows:

function Myisnan (x) {
return x!== x;
}

Currently a modified version of the isNaN Method Number.isnan () has been added to the ECMAScript 6 (translator note: Firefox has been implemented). This method of Crockford implementation is easier to understand than the Myisnan above, and the core code is this:

Copy Code code as follows:

Number.isnan = function (value) {
return typeof value = = = ' Number ' && isNaN (value);
};

2.Infinity

Dividing by 0 will produce another special value infinity:

Copy Code code as follows:

> 3/0
Infinity

You can't take for granted the calculated result of positive infinity or negative infinity:

Copy Code code as follows:

>infinity-infinity
NaN

A value larger than infinity is still infinitely large:

Copy Code code as follows:

> Infinity + Infinity
Infinity> 5 * Infinity
Infinity

3. For reference

What is {} + {} in JavaScript?