Don't replace (function(){})(); with !function(){}(); unless the return value isn't used

[Daniel-Hug]

I use UglifyJS to compress and mangle my JS and stick it in a bookmarklet.

This is the bookmarklet's JS (the anon function is to make sure it evaluates to undefined):

(function() {
  /*bookmarklet stuff*/
})();

This is the JS after compression (notice the exclamation point):

!function(){/*bookmarklet stuff*/}();

The exclamation point negates the return value of the anon function so instead of evaluating to undefined, it will evaluate to true. Then when I prepend the javascript: "protocol" the bookmarklet instead navigates to a blank page displaying true.

IMO UglifyJS shouldn't negate anonymous functions if the return value is used or in this case if the function is the root function.

[michaelficarra]

Related: estools/esmangle#78

[rvanvelzen]

I would say adding -c negate_iife=false would fix this.

[mishoo]

In general I think we prefer the current behaviour, and when you're building for a bookmarklet you can pass -c negate-iife=false as @rvanvelzen suggested.