How do I explain JavaScript closures to a child?

Beelzebub has asked you and your 11 friends to paint each of of 10000 balls 9 different colors or else ... Since it will take too long to paint by hand, all 12 of you invoke the ancient spirit Klevarius. Klevarius is fantabulastically powerful. The problem is he will grant you only one wish and he can't paint. You all think and thunk. Then ... ideation! You ask clevarius for a magic wand to create woodoo wands. Point the magic wand at a color and say "monochromaticate!" and a woodoo wand will materialize. The woodoo wand, paints anything it is pointed at, in the color the magic wand was pointing to when creating the woodoo wand. If you point the magic wand at an octarine colored tree, the woodoo wand created will paint anything in octarine. The 12 of you thank Klevarius, create 12 woodoo wands and paint happily ever after. Now, each of the woodoo wands is like a closure. When you created them, you did not put the color inside it. You just referred to the color it should paint. The woodoo wand holds the color it had to paint with itself. There is also "bichromaticate!" which would have created a woodoo wand which can paint anything two colors. Both colors have to be pointed at one after the other. In this case too, the woodoo wand is only referring to the colors pointed at when it was created. The real magic is the color[s] staying inside the woodoo wands and outside of it at the same time. If the original color pointed at was already magicked and owned by someone else, both of you can change colors on each other. The color variable was already bound. Pure woodoo wands and closures needs free colors and free variables.   A closure is something which holds for itself parts of the environment around it when it was was created and uses those parts when needed.

Why the hell would you explain closure to a kid and that too in javascript? but yeah, if you were to explain it to some one new to the concept of closures, a good example could be this. Every time you watch the winning moment of your favourite sports team, you get reminiscent of the emotions you had when you saw the match live on television. The match is already over, but you still get those feelings every single time you repeat the action of watching the winning moments. Yes because when the video  was being captured it, captured those beautiful memories as a separate copy! The phenomena of getting the same effect every time after watching a video that has captured some emotional moments of an event that has already occurred in past is called closure. In case you manage to get this idea into the head of a child, when he grows up show this piece of code to him: function createVideo(title, source){   var _video = new Video(title,source)   return {             "title": title              "playVideo : function(){                                   _video.play(); /* won't be in the scope after createVideo gets over but will still remember the contents of title and _video. */                                 }          } } // while match is going on var recorded = createVideo("Final, ICC Cricket World Cup, 2011",liveStream); .... .... .... //After some time .... .... .... recorded.playVideo();// will play the video that was recorded some time back!

Closures and the behavior you describe in your question are useful because functions can be passed as values to other parts of code. Like you're 5: You are doing great in school. Soon you'll go to a new school where they'll teach you how to be a carpenter. You'll take a lot of time to learn this single function (building things with wood). They'll give you a tool chest with a hammer and a saw and a bunch of other nice things for doing your function. They'll even give you access to the secret book of carpenter measurement conversions that only students of the school have access to. And most of all they'll teach you how to be a good carpenter. Then when you graduate you'll move far away with your toolbox, to a place where they need more carpenters. Probably somewhere in Alaska or Wyoming. When you get asked to do a job you'll need to do a bunch of things. Your tool box is yours, it's a set of "local" objects that you have access to. So you cut some stuff with your saw and hammer some stuff with your hammer. But then suddenly you need to make a measurent conversion. You don't remember what the numbers are and you don't own a copy of the secret book (there's only one copy in the world!). So you call up the school and ask them to look it up for you. They recognize you as a former student, say hello, and happily look up the numbers in the secret book. You continue on making the best darn rocking horse that Northern Iowa has ever seen. Another carpenter in town is very jealous because while he has a nice toolbox, he didn't come from a school that had access to the secret book. You both do the same thing in the same place, but you still have access to things from where you came from. That proves to be very helpful to you because there were too many carpenters where you came from, and you needed to be sent out to do work. ------ There is a lot of subtle trivia around things like when a function is "closed" and most people get that wrong (it's at execution time). However skipping the trivia, the most common use of closures I see is in event handlers. ` var what_to_alert = 5; somebutton.addEventListener('click', function() {   alert(what_to_alert); }); ` The function gets passed to a totally new part of the codebase as "the thing to run when the button gets clicked" but it can still remember the number that it's supposed to alert when that finally happens (it could be 10 minutes later when the button finally gets clicked. The action is just stored for later for when the event finally happens). Hope that helps!

A closure, in Javascript, allows you to create a function that is tied to a variable for later use. Here's a simple example: var sendMessageTo = function (name) { return function (message) { console.log ("Message for " + name + ": " + message); } }; var messageForRahul = sendMessageTo ("Rahul"); var messageForGreg = sendMessageTo ("Greg"); messageForRahul ("Hello, Rahul"); messageForGreg ("Hello, Greg"); When sendMessageTo is passed "Rahul" it binds it to the variable in the function that is returned. Each function will have a unique environment so the output will be: Message for Rahul: Hello, Rahul Message for Greg: Hello, Greg This is a trivial example but I hope it's easy to see how you can build functions this way that can solve more complicated problems.

Normally when you call a function it can create some temporary numbers or some strings in the computer memory, and do stuff with them to get at the desired answer. Once it's got the answer, all those temporary numbers and strings are forgotten about. But what if the answer you computed is itself a function, that does stuff with those temporary numbers that are normally supposed to go away? What if you then call that function? The computer could just say, "Dude! This function you're calling is messing around with values that I've already forgotten about, that won't fly!" But as it turns out, it can be very useful to allow such values to persist, so that you can have functions with access to some stashed away information. The prototypical example is making a counter: function makeCounter { var counter = 0; // this variable should normally go away, but it won't return function() { counter++; return counter; } } var getCount = makeCounter(); // the function makeCounter has finished, so normally var counter // would have been forgotten about! var n1 = getCount(); // n1 now equals 1 var n2 = getCount(); // n2 now equals 2 So you see that the variable 'counter' is not destroyed as it normally would be when  makeCounter has run its course, but it stays around and can be usefully used by getCount.

Here is my take at explaining a closure to a child. (Warning, it does not contain code examples, since I presume this child is normal and would rather play outside.)Imagine your brother (or sister) is trying to figure out how to draw a horse.Instead of having to guess how to draw the horse, your mom, who is your parent has a picture of the horse you can use.Every time you decide to draw a horse, you can ask your mom for access to that picture.Your ability to ask for the picture from your mom so you can carry out your function, to draw the horse, That's like a closure. Hahah nice try, but naming a function 'cookie' does not make it easier to understand for a child. :) Adult explanation can be found herehttp://www.masterjavascript.io/blog/2016/04/24/understanding-closures/