Promises

09_Advance_One/promises.js

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+//  A Promise is an object representing the eventual completion or failure of an asynchronous operation. 
+
+const promiseOne = new Promise(function(resolve, reject){
+    // Do an async task 
+    // DB calls, cryptography , network calls
+    setTimeout(function(){
+        console.log('Asyc task is complete');
+    },1000)
+});
+
+promiseOne.then(function(){
+    console.log("Promise Consumed");
+
+})
+
+new Promise(function(resolve, reject){
+    setTimeout(function(){
+        console.log("Async task 2");
+        resolve()
+    }, 1000)
+
+}).then(function(){
+    console.log("Async 2 resolved");
+})
+
+const promiseThree = new Promise(function(resolve, reject){
+    setTimeout(function(){
+        resolve({username: "Anjali", email: "[email protected]"})
+    }, 1000)
+})
+
+promiseThree.then(function(user){
+    console.log(user);
+})
+
+const promiseFour = new Promise(function(resolve, reject){
+    setTimeout(function(){
+        let error = true
+        if (!error) {
+            resolve({username: "anjali", password: "123"})
+        } else {
+            reject('ERROR: Something went wrong')
+        }
+    }, 1000)
+})
+
+ promiseFour       // For better code readability use then in the new line 
+ .then((user) => {
+    console.log(user);
+    return user.username
+}).then((username) => {
+    console.log(username);
+}).catch(function(error){
+    console.log(error);
+}).finally(() => console.log("The promise is either resolved or rejected"))
+ // Finally executes always 
+
+
+const promiseFive = new Promise(function(resolve, reject){
+    setTimeout(function(){
+        let error = true
+        if (!error) {
+            resolve({username: "javascript", password: "123"})
+        } else {
+            reject('ERROR: JS went wrong')
+        }
+    }, 1000)
+});
+
+
+// Same function but using try and catch block for error handling 
+async function consumePromiseFive(){
+    try {
+        const response = await promiseFive
+        console.log(response);
+    } catch (error) {
+        console.log(error);
+    }
+}
+
+consumePromiseFive()
+
+// async function getAllUsers(){
+//     try {
+//         const response = await fetch('https://jsonplaceholder.typicode.com/users')
+
+           // Data comes here in string format we are changing it to the json format below 
+//         const data = await response.json()
+//         console.log(data);
+//     } catch (error) {
+//         console.log("E: ", error);
+//     }
+// }
+
+//getAllUsers()
+
+fetch('https://github.com/AnjaliUp')
+.then((response) => {
+    return response.json()
+})
+.then((data) => {
+    console.log(data);
+})
+.catch((error) => console.log(error))
+
+// promise.all
+// yes this is also available, kuch reading aap b kro.