How to access an object property using a variable containing its key name

Question

I think that this is not possible in JS but I thought I would double check before moving on.

I have created a simple prototype on my array object, its purpose is to sort the array by a key value.

The function is working correctly however I want to make it a bit more reusable, by passing in a key into the function. However when I pass in a value it is a string so does not reference correctly. Does any one know how to solve this problem so in my example below I can sort by the passed in key1 not the hard-coded key1.

My code is this and a fiddle is up here http://jsfiddle.net/9KLk8/1/

  Array.prototype.keySort=function(key1)
    {
      this.sort(function(a,b) {return (a.height > b.height) ? 1 : ((b.height > a.height) ? -1 : 0);} );
    }
    var a1 = [ 
            { key: 1, height : 100     },
            { key: 2,    height: 700  },
            { key: 3, height: 200 }
        ];
    a1.keySort("height");
    console.log(a1);

Answer 1

Use the brackets syntax:

Array.prototype.keySort=function(key1)
{
    this.sort(function(a,b) {return (a[key1] > b[key1]) ? 1 : ((b[key1] > a[key1]) ? -1 : 0);} );
}

Jsfiddle: http://jsfiddle.net/2hb4K/

Answer 2

Yes, you can do this, because with JavaScript, you can access properties either with dotted notation and a literal ( a.height ), or with bracketed notation and a string ( a["height"] ). In the latter case, the string doesn't have to be a literal string, it can be the result of any expression, including a variable reference.

So a[key1] would access the property named by the key1 variable.