promises understanding

Author: INDRESH-009

js_notes/cohertnotes/week2/buildingpromise.js

@@ -0,0 +1,64 @@
+//callback hell
+/*function callbackHell(){
+    setTimeout(()=> {
+        console.log("Callback 1");
+        setTimeout(()=> {
+            console.log("Callback 2");
+            setTimeout(()=> {
+                console.log("Callback 3");
+                setTimeout(()=>{
+                    console.log("Callback 4");
+                },3000)
+            },2000)
+        },1000)
+    },1000)
+}
+callbackHell();
+//In the above example we are using an async function setTimeout and passing an arrow function as a parameter , Thus when a function is passes into another function as parameter it is called as callback function 
+//Callbacks inside callbacks create an ugly syntax and pyramid of dooom , to avoid this we use promises 
+
+const p = new Promise (function(resolve){
+    let output = setTimeout(()=>{
+        console.log("Callback 1");
+        resolve(output);
+    },1000)
+})
+p.then(function(resolve){
+    setTimeout(()=>{
+        console.log("Callback 2")
+    },10000);
+})
+.then(function(resolve){
+    setTimeout(()=>{
+        console.log("Callback 3")
+    },1000);
+})
+console.log(p);
+*/
+
+const pro = new Promise(function(resolve) {
+    let output = setTimeout(() => {
+        console.log("Callback 1");
+        resolve(output); // Resolving with the timeout ID
+    }, 1000);
+});
+
+pro.then(function(output) { // Using the resolved value from the Promise
+    return new Promise(function(resolve) {
+        setTimeout(() => {
+            console.log("Callback 2");
+            resolve(); // Resolving without a value
+        }, 10000);
+    });
+})
+.then(function() {
+    return new Promise(function(resolve) {
+        setTimeout(() => {
+            console.log("Callback 3");
+            resolve(); // Resolving without a value
+        }, 1000);
+    });
+});
+
+console.log(pro); // Logging the Promise object
+

js_notes/js_hithesh.js/lec3.js

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+function shout(str){
+    return console.log(str + str);
+}
+shout('Fire');