Include Javascript files in CRM (load custom javascript file)

Some time user required to do same type of work at multiple place in JavaScript, for this user have two options either place a same type of code at all the places or store the same code at one place in JavaScript file and name it with "xyz.js", now the question is how to use this JS file in different entities from CRM.

Some steps are there:
1) create one folder with name "myscripts" in ISV in CRM server.
2) place the "xyz.js" file in above named folder.
3) use the following JavaScript code at the OnLoad event of the entity.

var script = document.createElement('script');
script.language = 'javascript';
script.src = '/ISV/myscripts/xyz.js';
document.getElementsByTagName('head')[0].appendChild(script);

var f = function()
{
if (event.srcElement.readyState == "loaded")
{
//perform onload scripts
FunctionfromJavaScriptFile();
// some function from your custom js file
}
}
script.attachEvent("onreadystatechange", f);

After using above three defined steps you are ready to call custom JavaScript file.