Specific real life application of closures in javascript

I have used JS for two years and my pluralsight accessment rates me as proficient in JS, I understand prototypical inheritance, higher order functions, IIFEs etc and I have used them in real world instances but closures is one of those concept that you understand but can't find any reason why you would want to use them in real world development, I mean I know that if I say,

function expClosure(val){
   //do something to val-->anotherVal
   return function(val){return anotherVal)};
}
var exp = expClosure(val);
exp(); --> returns the value of anotherVal;

My question is why would I want to do this, or rather what specific instances can lead me to consider using this.

Answer

The main benefit to closures is you can "partially apply" a function using a closure, then pass the partially applied function around, instead of needing to pass the non-applied function, and any data you'll need to call it (very useful, in many scenarios).

Say you have a function f that will need in the future 2 pieces of data to operate. One approach is you could pass both pieces in as arguments when you call it. The problem with this approach is if the first piece of data is available immediately, and the second isn't, you'll have to pass it around with f so it's in scope when you want to call the function.

The other option is to give the available data to the function immediately. You can create a closure over the data, have the function reference the external data, then pass the function around by itself.

Option 2 is much simpler.

You can also use closures to implement static variables in functions in languages that don't natively support them. Clojure (the language) implements it's memoize function by having it return a modified version of the passed function that holds a reference to a map representing argument/return value pairs. Before the function is run, it first checks if the arguments already exist in the map. If they do, it returns the cached return value instead of recalculating it.

(Adapted from my answer to another question)