Useless use of document.write
While reviewing some enterprise JavaScript for a client I came across a couple of these inside if clauses:
document.write("<scr"+"ipt language=javascript>var some_var = 'some value'<" + "/scr"+"ipt>");
There’s definitely some room for improvement here. For one, the language attribute on the <script> element is obsolete in HTML; it can safely be omitted.
document.write("<scr"+"ipt>var some_var = 'some value'<" + "/scr"+"ipt>");
Next, there’s no need to concatenate the string like that — you can just write it out all at once, as long as you escape the </script> end tag:
document.write("<script>var some_var = 'some value'<\/script>");
There are only few good reasons to ever use document.write. Writing out <script> elements can be one of them, but in this case? Not so much. Believe it or not, the intention of this code snippet was to create a global variable. (Polluting the global scope with variables is something that should be avoided whenever possible; however, in this case, the variable really needed to be global.)
Of course, there’s a better way to do that in client-side JavaScript:
window.some_var = 'some value';