JavaScript Promise and Promise Chaining
The Complete Guide:
Thread 🧵
The Complete Guide:
Thread 🧵
📌In JavaScript, a promise is a good way to handle asynchronous operations. It is used to find out if the asynchronous operation is successfully completed or not.
📌A promise may have one of three states.
1⃣Pending
2⃣Fulfilled
3⃣Rejected
📌A promise may have one of three states.
1⃣Pending
2⃣Fulfilled
3⃣Rejected
📌Create a Promise.
➡️To create a promise object, we use the Promise() constructor.
➡️The Promise() constructor takes a function as an argument. The function also accepts two functions resolve() and reject().
➡️To create a promise object, we use the Promise() constructor.
➡️The Promise() constructor takes a function as an argument. The function also accepts two functions resolve() and reject().
➡️If the promise returns successfully, the resolve() function is called. And, if an error occurs, the reject() function is called.
📌JavaScript Promise Chaining.
➡️Promises are useful when you have to handle more than one asynchronous task, one after another. For that, we use promise chaining.
➡️You can perform an operation after a promise is resolved using methods then(), catch() and finally().
➡️Promises are useful when you have to handle more than one asynchronous task, one after another. For that, we use promise chaining.
➡️You can perform an operation after a promise is resolved using methods then(), catch() and finally().
📌JavaScript then() method.
➡️The then() method is used with the callback when the promise is successfully fulfilled or resolved.
➡️The then() method is used with the callback when the promise is successfully fulfilled or resolved.
📌JavaScript Promise Versus Callback.
➡️Promises are similar to callback functions in the sense that they both can be used to handle asynchronous tasks.
➡️Promises are similar to callback functions in the sense that they both can be used to handle asynchronous tasks.
📌Their differences can be summarized in the following points:
➡️JavaScript Promise
📝The syntax is user-friendly and easy to read.
📝Error handling is easier to manage.
➡️JavaScript Callback
📝The syntax is difficult to understand.
📝Error handling may be hard to manage.
➡️JavaScript Promise
📝The syntax is user-friendly and easy to read.
📝Error handling is easier to manage.
➡️JavaScript Callback
📝The syntax is difficult to understand.
📝Error handling may be hard to manage.
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