How to add and item to array only if it doesnt exist already using javascript?

Question

i have an array called myarray[]. How i can add item to myarray only if that item already doesn't exist in array ?

  myarray.push({ url: urlValue, filename: fileNameValue });

Edited: i tried following but i get double pushed data after 3th push:

if (files === undefined || files.length == 0)
        {

           myarray.push({ url: urlValue, filename: fileNameValue });

        }

    for(var g=0; g<myarray.length; g++){
            if(myarray[g].url == urlValue)
            {
              alert('already in array');
            }
            else
            {

                   myarray.push({ url: urlValue, filename: fileNameValue });

            }//end of else
           }//end of for loop