

Conversions in Javascript - vetri02
http://thetascript.com/conversions-in-javascript/

======
Stratoscope
This article has a few problems.

* "All of the above does the same job...". Not true at all; the four examples do three very different things. Try them with a more interesting string argument, say '012.78':
    
    
      parseInt('012.78')  // 10 (number interpreted as octal integer)
      Number('012.78')    // 12.78
      +'012.78'           // 12.78
      ~~(1*'012.78')      // 12
    

* "...and n1==n2==n3==n4" Using == instead of === here makes the statement meaningless. After all, this is also true:
    
    
      '12' == 12
    

* The "wicked" method, ~~( 1 * '12' ), smacks of cargo cult programming. No mention of the fact that it uses two operators instead of one? Why not test the two separately:
    
    
      1*'012.78'  // 12.78
      ~~'012.78'  // 12
    

Complaints aside, the results for the "wicked" method certainly are
interesting. Why is it (along with the two variations above) so extremely fast
in Firefox?

Here's an updated jsperf with those additional test cases:

<http://jsperf.com/parsenumber/5>

~~~
some-1
The reason why the wicked is so fast in Firefox is because of the literal
string and the optimizations done by the compiler.

Try this (creates a function and then show the source):

    
    
      Function('return ~~(1 * "12");').toString();
    

And you get this result:

    
    
      "function anonymous() { return 12; }"
    

Notice that the expression has been converted to 12 in the function, so each
call to it will just return 12 instead of converting it. That's why it is so
much faster. The same is true for "<<", ">>" and "1 * '12'"

I created another test where it actually do the conversion, by assigning the
string to a variable and use that in each test. There parseInt is faster in
Firefox, Opera, Chrome and Safari. Surprisingly it is the slowest in IE, where
+str is the fastest.

You can find it here: <http://jsperf.com/parse-number-from-string>

Also notice:

* All the logical operators (~, <<, >>, |) operates internally on a 32 bit signed integer, while parseInt, Number and + operates on a 64 bit signed float. Try to convert 2147483648 or 2333444555 for a little surprise.

* At the other jsperf someone added "0+'12'". That returns a string, not a number.

~~~
Stratoscope
Ah, thank you very much. This is one of those things that is so obvious in
hindsight: don't run performance tests using constant values, or the compiler
may optimize the code away!

------
FuzzyDunlop
One might prefer to supply the radix when using parseInt(), too. Lest one
encounters strings that convert into octal numbers.

parseInt('09') !== parseInt('9')

------
cygx
Except for n2 and n3, all of these have different semantics.

Performance doesn't help if your code is wrong.

------
turshija
Firefox results are amazing, "wicked" is over 20x faster then any other method
...

------
froball
Why people are so keen on micro-optimizing their code? The bottleneck lies on
DOM, not on your conversions.

~~~
Herover
I guess that depends on what you are doing.

If you have a 10k csv file and want to make a graph using javascript, I
believe it could come handy.

