Question

I want to create an associative array:

var aa = {} // Equivalent to Object(), new Object(), etc... 

And I want to be sure that any key I access is going to be a number:

aa['hey'] = 4.3; aa['btar'] = 43.1; 

I know JavaScript doesn’t have typing, so I can’t automatically check this, but I can ensure in my own code that I only assign strings to this aa.

Now I’m taking keys from the user. I want to display the value for that key. However, if the user gives me something like "toString", the user gets back a function, not an int! Is there a way to make sure any string the user gives me is only something I define?

Is the only solution something like the following?

delete aa['toString']; delete aa['hasOwnProperty']; 

etc…

Answer 1

This may work for you:

function getValue(id){   return (!isNaN(aa[id])) ? aa[id] : undefined; } 

Alternatively, I recommend this generic solution:

function getValue(hash,key) {     return Object.prototype.hasOwnProperty.call(hash,key) ? hash[key] : undefined; } 

Note the following: The key will internally be converted to a string because the key is actually a name of an attribute.

var test = {   2: "Defined as numeric",   "2": "Defined as string" }  alert(test[2]); // Alerts "Defined as string" 

If trying to use an object:

var test = {}, test2 = {}; test[test2] = "message"; // Using an object as a key.  alert(test[test2]); // Alerts "message". It looks like it works...  alert(test[test2.toString()]); // If it really was an object this would not have worked, // but it also alerts "message". 

Now that you know that it is always a string, let’s use it:

var test = {};  var test2 = {     toString:function(){return "some_unique_value";}     // Note that the attribute name (toString) don't need quotes. }  test[test2] = "message"; alert(test["some_unique_value"]); // Alerts "message".