Question

I have the following javascript object literal (excerpt)

var foo = {"hello[35]":100,"goodbye[45]":42};

I have the following query:

var query = "hello"

I would like to call foo[query] to obtain the value 100, but there is a [35] for which I don’t necessarily know the value of. I know for sure that I will get a unique match. Is there any way to input query is some kind of javascript regular expression? i.e.

Regex = /hello/
foo[Regex]
100

pardon the noob question…

Answer 1

What you have here:

var foo = {"hello[35]":100,"goodbye[45]":42};

is not JSON, which is a string representation of an object; what you have is an object literal, which creates an actual JavaScript object. As far as I know the only way to retrieve a value from an object by matching a property name with a regex is to enumerate the property names and test each one. The regex you’ll need is something like:

/^hello(\[\d*\])?$/

…which will match against “hello” optionally followed by zero or more digits in square brackets. But you don’t want to hard code “hello” given that you also (presumably) need the “goodbye” value, so use a function:

function getPropertyByRegex(obj,propName) {
   var re = new RegExp("^" + propName + "(\\[\\d*\\])?$"),
       key;
   for (key in obj)
      if (re.test(key))
         return obj[key];
   return null; // put your default "not found" return value here
}

var foo = {"hello[35]":100,"goodbye[45]":42};

alert(getPropertyByRegex(foo, "hello"));    // 100
alert(getPropertyByRegex(foo, "goodbye"));  // 42
alert(getPropertyByRegex(foo, "whatever")); // null (not found)

Demo: http://jsfiddle.net/asDQm/