CodePen

HTML

            
              
            
          
!

↑ Insert the most common viewport meta tag

CSS

            
              
            
          
!
? ?
? ?
Must be a valid URL.
+ add another resource
via CSS Lint

JS

            
              > function f() {
...   function g(){
...       return this;
...   }
...   return g()
...}
> o = {f:f}
> o.f() == window
true
> o.f() == o
false
            
          
!
Must be a valid URL.
+ add another resource
via JS Hint
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