Analogous to a cascading stylesheet, JavaScript can be compressed by removing spaces, backslashes, and new lines.

function displayDate()
{
  document.getElementById("demo").innerHTML=Date();
}
displayDate(){document.getElemById("demo").innerHTML=Date()}

The file has been reduced by 5 characters which means 6.49 percent saved. On a very large JavaScript file, such as libraries, this will be very effective.

The base 62 is a positional notation. A positional notation is a method of representing encoded numbers and it can be used to represent a very long test by a shorter version. Using the base 62 will reduce the time to download the file but will add an extra step before the customer can use it. Indeed, the client has to decode the encoded JavaScript. The previous function in base 62 is equal to the following function:

eval(function(p,a,c,k,e,r){e=String;if[…]))

For the sake of readability, we will not put the whole of base 62 encoding here. But, before applying this technique to your JavaScript files, you have to compare the reduction in time for downloading the script to the extra time taken to execute it.

There are some known issues when you use JavaScript merging and other JavaScript libraries ,such as jQuery integrated in Magento. Most of the time the issues come from bad integration.