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Declaring the same global variable multiple times

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  Declaring the same global variable multiple times "Joey@still_Learning.invalid" <Joey@still_Learning.invalid> - 2015-06-07 08:13 -0700
    Re: Declaring the same global variable multiple times Steven D'Aprano <steve@pearwood.info> - 2015-06-08 01:56 +1000
    Re: Declaring the same global variable multiple times Denis McMahon <denismfmcmahon@gmail.com> - 2015-06-07 21:14 +0000
      Re: Declaring the same global variable multiple times "Joey@still_Learning.invalid" <Joey@still_Learning.invalid> - 2015-06-07 17:33 -0700
        Re: Declaring the same global variable multiple times Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2015-06-08 08:56 +0200
          Re: Declaring the same global variable multiple times "Joey@still_Learning.invalid" <Joey@still_Learning.invalid> - 2015-06-08 07:28 -0700
          Re: Declaring the same global variable multiple times "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-06-08 17:03 +0200
          Re: Declaring the same global variable multiple times Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2015-06-08 19:09 +0200
    Re: Declaring the same global variable multiple times "Joey@still_Learning.invalid" <Joey@still_Learning.invalid> - 2015-06-07 14:23 -0700

#28024 — Declaring the same global variable multiple times

I have an extensive script that often generates the same global
variable in multiple functions. I declare each a global by defining as
window.variable = xxx.

Do multiple declarations require greater compiling or otherwise
overhead, i.e., performance degradation?

Instead of re-declaring should I declare 'var xxx' outside the
functions? Does this accomplish the same as above?

TIA,
-- 
Joey

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#28025

On Mon, 8 Jun 2015 01:13 am, Joey@still_Learning.invalid wrote:

> I have an extensive script that often generates the same global
> variable in multiple functions. I declare each a global by defining as
> window.variable = xxx.
> 
> Do multiple declarations require greater compiling or otherwise
> overhead, i.e., performance degradation?


Surely this is premature optimization? Unless the calculation of xxx is
horribly expensive, or you are performing it millions of times, I find it
hard to believe that this could be anything more than a micro-optimization
(shaving a few hundredth of a millisecond off the runtime or so).


> Instead of re-declaring should I declare 'var xxx' outside the
> functions? Does this accomplish the same as above?

It seems to me that an outer declaration should be preferred, not because it
is "more efficient to run", but because it is more readable, more
understandable, and more easily maintained. If you decide to change it from
variable = xxx to variable = yyy, you only need to change one place,
instead of twenty.


-- 
Steven

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#28034

On Sun, 07 Jun 2015 08:13:50 -0700, Joey@still_Learning.invalid wrote:

> I have an extensive script that often generates the same global variable

Why are you using global variables? Unless you can answer this question 
in a convincing manner, you probably shouldn't be using global variables.

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#28038

On Sun, 7 Jun 2015 21:14:23 +0000 (UTC), Denis McMahon
<denismfmcmahon@gmail.com> wrote:

>On Sun, 07 Jun 2015 08:13:50 -0700, Joey@still_Learning.invalid wrote:
>
>> I have an extensive script that often generates the same global variable
>
>Why are you using global variables? Unless you can answer this question 
>in a convincing manner, you probably shouldn't be using global variables.

I use the same variables with the same values in multiple functions.
Instead of recomputing in each function, I compute once to a global. 
-- 
Joey

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#28041

On 2015-06-08 02:33, Joey@still_Learning.invalid wrote:
> On Sun, 7 Jun 2015 21:14:23 +0000 (UTC), Denis McMahon
> <denismfmcmahon@gmail.com> wrote:
>
>> On Sun, 07 Jun 2015 08:13:50 -0700, Joey@still_Learning.invalid wrote:
>>
>>> I have an extensive script that often generates the same global variable
>>
>> Why are you using global variables? Unless you can answer this question
>> in a convincing manner, you probably shouldn't be using global variables.
>
> I use the same variables with the same values in multiple functions.
> Instead of recomputing in each function, I compute once to a global.

Instead of that you may create singleton which can store your data in a 
property and add method to get/set values.

Example:

var example = {

     sharedVariable: undefined,

     getValue : function () {
         return this.sharedVariable
     },

     setValue : function (value) {
         this.sharedVariable = value;
     }

};

There are many other ways to avoid using global variables.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

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#28042

On Mon, 08 Jun 2015 08:56:54 +0200, Cezary Tomczyk
<cezary.tomczyk@gmail.com> wrote:

>On 2015-06-08 02:33, Joey@still_Learning.invalid wrote:
>> On Sun, 7 Jun 2015 21:14:23 +0000 (UTC), Denis McMahon
>> <denismfmcmahon@gmail.com> wrote:
>>
>>> On Sun, 07 Jun 2015 08:13:50 -0700, Joey@still_Learning.invalid wrote:
>>>
>>>> I have an extensive script that often generates the same global variable
>>>
>>> Why are you using global variables? Unless you can answer this question
>>> in a convincing manner, you probably shouldn't be using global variables.
>>
>> I use the same variables with the same values in multiple functions.
>> Instead of recomputing in each function, I compute once to a global.
>
>Instead of that you may create singleton which can store your data in a 
>property and add method to get/set values.
>
>Example:
>
>var example = {
>
>     sharedVariable: undefined,
>
>     getValue : function () {
>         return this.sharedVariable
>     },
>
>     setValue : function (value) {
>         this.sharedVariable = value;
>     }
>
>};
>
>There are many other ways to avoid using global variables.

Thank you.
-- 
Joey

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#28044

Stefan Ram wrote:

> Cezary Tomczyk <cezary.tomczyk@gmail.com> writes:
>> Instead of that
> 
>   (that = a global)
> 
>>                you may create singleton which can store your data in a 
>> property and add method to get/set values.
>> Example:
>> var example = {
>>     sharedVariable: undefined,
> 
>   And »example« is what? Not a global?

Basically, `example` is a global, but the namespace pattern helps to
*reduce* the number of globals.  To *avoid* globals, IIFEs or the module
pattern might be more appropriate.

-- 
Christoph M. Becker

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#28046

On 2015-06-08 16:56, Stefan Ram wrote:
> Cezary Tomczyk <cezary.tomczyk@gmail.com> writes:
>> Instead of that
>
>    (that = a global)
>
>>                 you may create singleton which can store your data in a
>> property and add method to get/set values.
>> Example:
>> var example = {
>>      sharedVariable: undefined,
>
>    And »example« is what? Not a global?

Yes, example is in global context. However, still better than defining 
more than one global variable.

On the other hand I would encapsulate it with AMD pattern:

define(function(){

    var example = {};

    return example;

});

but that's different story.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/

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#28035

On Sun, 07 Jun 2015 08:13:50 -0700, "Joey@still_Learning.invalid"
<Joey@still_Learning.invalid> wrote:

>I have an extensive script that often generates the same global
>variable in multiple functions. I declare each a global by defining as
>window.variable = xxx.
>
>Do multiple declarations require greater compiling or otherwise
>overhead, i.e., performance degradation?
>
>Instead of re-declaring should I declare 'var xxx' outside the
>functions? Does this accomplish the same as above?
>
Thanks, Steven and Stefan. External it is.
-- 
Joey

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