Question

I get some json data, and there I have such a structure:

'modules' : {
    'category1' : {
        'section1' : {
             'page1' : [ 'module1', 'module2' ]
        },
        'section2' : {
             'page1' : [ 'module1' ]
        }
    },
    // and so on
}

I need to get all modules of some page.

Input parameters are category, section and page.

So i need to get modules[category][section][page].

But what if there are no modules for such a section, or page.

    // m = getAllModules();

    if ( m.hasOwnProperty(category) ) {
        if ( m[category].hasOwnProperty(section) ) {
            if (m[category][section].hasOwnProperty(page)) {
                concrete = m[category][section][page];
            }
        }
    }

How to optimize this script? It’s lot of calls of m[]. Is there a better(faster) way to do this?

Answer 1

You could do it like this:

var categories, sections;    
if ((categories = modules[categoryName]) && (sections = categories[sectionName])) {
  concrete = sections[pageName] || [];
}
else {
  concrete = [];
}

You could also create a more general solution:

function traverse(source) {
  var path = Array.prototype.slice.call(arguments, 1);
  var current = source;
  for (var i = 0, l = path.length; i < l; ++i) {
    current = current[path[i]];
    if (!current) break; 
  }
  return current;
}

Use it like this:

concrete = traverse(modules, categoryName, sectionName, pageName) || [];