[Laszlo-dev] Javascript optimization hints [Was: [Laszlo-checkins] r5888 - in openlaszlo/branches/wafflecone: WEB-INF/lps/lfc/data WEB-INF/lps/lfc/events WEB-INF/lps/lfc/views lps/components/base]

[P T Withington]

Sorry, no.  You can't make type decls yet.

On 2007-08-01, at 11:47 EDT, Max Carlson wrote:

> Thanks for the tips - it's always good to have a reminder :).
>
> Just so I'm clear, we can now use JS2 type declarations:
>
> var uplinkArray: Array;
>
> but they'll be ignored (for now).  Is this correct?
>
> If so, it'll be a good task for someone to go through the LFC and  
> add type annotations sooner rather than later!
>
> P T Withington wrote:
>> Since the compiler does not do common-subexpression elimination,  
>> when you are trying to optimize things, pretend you are writing in  
>> 1985 C.  Instead of:
>>   if (d.c[d.f]) d.c[d.f]( sd )
>> say:
>>   var f = d.c[d.f];
>>   if (f) f(sd);
>> Even better, when you find yourself having to write a null check,  
>> ask yourself if it would be cleaner, simpler, and more efficient  
>> to have the variable you are referencing not be nullable.  For  
>> instance, if a variable is an array, consider using an empty array  
>> for its initial value, rather than null.  This is a time/space  
>> trade-off:  if there are many operations on the array and the  
>> variable is almost always not null, it will be more efficient to  
>> use an empty array; if there are few operations and the variable  
>> is usually null, then not allocating the empty array is the better  
>> choice.
>> (In Javascript 2, you will have the option of declaring a variable  
>> to be of a particular type, and you will have the option of  
>> declaring wether or not that variable can also be null.  If you  
>> declare it not to be nullable, then the compiler will give you a  
>> compile-time warning if it cannot prove that the variable is never  
>> null, and it will insert the appropriate runtime check for you.
>>   // This can be null, you have to check before using
>>   var uplinkArray: Array;
>>   // This cannot be null, you have to give a valid initial value
>>   var uplinkArray: Array! = new Array();
>> Even though we don't yet support the type declarations, we can  
>> follow the pattern and be ready...)
>
> -- 
> Regards,
> Max Carlson
> OpenLaszlo.org