complete E14

sohamsshah · sohamsshah · commit ace1086aa440 · 2021-03-03T13:19:32.000+05:30
diff --git a/NamasteJS/E14.md b/NamasteJS/E14.md
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+# [Episode 14](https://www.youtube.com/watch?v=lW_erSjyMeM&list=PLlasXeu85E9cQ32gLCvAvr9vNaUccPVNP&index=16): Callback Functions in JS ft. Event Listeners &#128293;
+
+
+### Callback Function in JS
+
+```
+setTimeout(function (){
+    console.log("timer");
+},5000);
+
+function x(y){
+    console.log("x");
+
+}
+x(function y(){
+    console.log("y");
+});
+```
+
+Output:
+>timer
+>x
+>y
+
+**Explanation**
+
+Settimeout is an async function; it takes a function and executes after x miliseconds.
+
+The JS thread continues to execute other code and the call stack is filled and emptied.
+
+Once the call stack is empty, it checks if the async queue is filled; then it executes those functions in the queue.
+
+Thus output is x, y and then timer.
+
+JS is single threaded synchronous language.
+
+### Important Interview Question
+
+```
+function attachEventListeners(){
+    let count=0;
+    document.getElementById("clickMe").addEventListener("click", console.log("Button", ++count));
+}
+
+attachEventListeners();
+```
+
+### removeEventListeners
+
+Event Listeners are memory-heavy. Thus we must use removeEventListeners.
+
+
