How to convert a string to variable name

Question

I'm loading several external JSON files and want to check if they have been successfully cached before the the next screen is displayed. My strategy is to check the name of the array to see if it an object. My code works perfectly when I check only a single array and hard code the array name into my function. My question is: how can i make this dynamic?

not dynamic: (this works)

$("document").ready(){
    checkJSON("nav_items"); 
}

function checkJSON(){

   if(typeof nav_items == "object"){
       // success...
   }

}

dynamic: (this doesn't work)

$("document").ready(){
    checkJSON("nav_items"); 
    checkJSON("foo_items"); 
    checkJSON("bar_items"); 
}

function checkJSON(item){

   if(typeof item == "object"){
       // success...
   }

}

here is the a larger context of my code:

var loadAttempts = 0;  
var reloadTimer = false;  



$("document").ready(){
    checkJSON("nav_items"); 
}



function checkJSON(item){

loadAttempts++;

//if nav_items exists
if(typeof nav_items == "object"){

        //if a timer is running, kill it
        if(reloadTimer != false){
        clearInterval(reloadTimer);
        reloadTimer = false;
    } 
    console.log("found!!");
    console.log(nav_items[1]);
    loadAttempts = 0; //reset

            // load next screen....                   

} 

//if nav_items does not yet exist, try 5 times, then give up!
else {
            //set a timer
    if(reloadTimer == false){
        reloadTimer = setInterval(function(){checkJSON(nav_items)},300);
        console.log(item + " not found. Attempts: " + loadAttempts );
    }
            else {
        if(loadAttempts <= 5){
            console.log(item + " not found. Attempts: " + loadAttempts          );
        } else {
            clearInterval(reloadTimer);
            reloadTimer = false;
            console.log("Giving up on " + item + "!!");
        }
    }
}

}

Rory McCrossan · Accepted Answer · 2014-06-06 09:22:34Z

2

Depending on the scope of the arrays you should be able to access them via window[]:

$("document").ready(function() {
    checkJSON("nav_items"); 
});

function checkJSON(item) {
   if (typeof window[item] == "object") {
       alert(item + ' is an object');
   }
}

Example fiddle

answered Jun 6, 2014 at 9:22

Rory McCrossan

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1 Comment

Anthony Garcia-Labiad Over a year ago

It would be better to use a specific object, for example called "cache", instead of putting lot of stuff in global namespace.

Balachandran · Accepted Answer · 2014-06-06 09:25:06Z

1

you have to pass the object ...not string .declare the variable and and assign the json value

checkJSON(nav_items); 
 checkJSON(foo_items); 
 checkJSON(bar_items);

answered Jun 6, 2014 at 9:25

Balachandran

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1 Comment

p1xelarchitect Over a year ago

That doesn't work because the object doesn't exist at the time the argument is passed, and so passing the object as a parameter will give me an error. nav_items is defined in an external JSON file that will take a few seconds to load. The purpose of my function checkJSON() is to wait for it to load and then notify me when the object exists.

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