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javascriptappjs

|| and onmessage in javascript

I am reading a open source project and it has a js file like this

var pipe = function(source, listeners){
    source.onmessage = function onmessage(msg){
           //.. do something ..
    };

    return {
      //.. something ...
    };
  }(nativeWindow || appjs, {});

What does (nativeWindow || appjs ) means where they both are objects ?

Does it mean that this function is called for both of them ?

Or it is merging both of these objects ?

And is this .onmessage is something standard thing like alert() or window ? What i mean by standard is that is there something happening behind the scenes in this .onmessage function or is it just like simple function ?

Thanks

Solution

  • if nativeWindow evaluates to false (e.g. if it's undefined) then appjs is passed in as source; otherwise nativeWindow is passed in as source. The property onmessage of whichever object ispassed in as source is then set to the onmessage function