Global Javascript Properties - memory usage

Question

I'm building various d3.js dashboards which frequently refer to a javascript_properties.js file which includes properties such as:

var all_charts = (function() {

   return {
     width:860,
     height:500,
     from_date:"",
     to_date:"",
     highlight_color:"#00FFFF"
   }

}());

I use these properties frequently within various functions.

My question is:

Is there any harm in calling each property direct every time I use it or would it be more efficient to declare a local variable at the beginning of each function if a property is going to be called more than once?

To show an example. A local variable:

 var width = all_charts.width;

OR calling

all_charts.width

as many times as required during a function.

There may be little discernible difference?

Make your code readable and don't worry about it, the effect is nonexistent related to the cost of other logic. — Etheryte
– Etheryte, Commented Sep 13, 2017 at 8:39

T.J. Crowder · Accepted Answer · 2017-09-13 08:45:56Z

3

This isn't about memory usage, it's about lookup time.

Yes, caching the property to a local variable may make it faster when using that repeatedly afterward, as the JavaScript engine doesn't have to traverse the scope chain up to the global level to find all_charts and then look up width on it.

But, it's unlikely to make a noticeable difference unless you're using these properties hundreds of thousands of times in the same function.

Side note: There's no point to the function in the all_charts code, what you have does exactly what this does, just more indirectly:

var all_charts = {
  width:860,
  height:500,
  from_date:"",
  to_date:"",
  highlight_color:"#00FFFF"
};

edited Sep 13, 2017 at 8:45

answered Sep 13, 2017 at 8:38

T.J. Crowder

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