Callbacks
Callback, EK, FUNCTION, hai, JO, EK, DUSRE, FUNCTION, ko, ARGUMENT, ke, ROOP, mein, PASS, kiya, jaata hai, aur, BAAD, mein, INVOKE, kiya, jaata hai — Node.js ki, EARLY, ASYNC, PATTERNS, mein, YE, STANDARD, THA.
Node.js, "ERROR-FIRST", CALLBACK, CONVENTION, USE, karta hai — CALLBACK, ka, FIRST, ARGUMENT, HAMESHA, ERROR, (ya, null) hota hai, DUSRA, ARGUMENT, RESULT, DATA, hota hai.
const fs = require("fs");
fs.readFile("data.txt", "utf8", (err, data) => {
if (err) {
console.error("Error:", err.message);
return;
}
console.log("Data:", data);
});
// Multiple, NESTED, callbacks — "callback hell":
fs.readFile("a.txt", "utf8", (err, a) => {
fs.readFile("b.txt", "utf8", (err, b) => {
console.log(a + b); // deeply, NESTED — hard to read
});
});- Callback = function, jo, ARGUMENT, ke, ROOP, mein, PASS, hota hai
- Node.js, "error-first" convention, USE, karta hai — (err, data)
- Deeply nested callbacks, "callback hell" ka, PROBLEM, banaте, HAIN
util.promisify(), Node.js, ka, BUILT-IN, UTILITY, hai, JO, ERROR-FIRST, CALLBACK-STYLE, FUNCTIONS, ko, Promise-RETURNING, FUNCTIONS, mein, CONVERT, karta hai — LEGACY, CALLBACK-BASED, APIs, ko, MODERN, async/await, ke, saath, USE, karne, ke, liye, USEFUL, hai.
const util = require("util");
const fs = require("fs");
const readFileAsync = util.promisify(fs.readFile);
const data = await readFileAsync("data.txt", "utf8");DEEPLY, NESTED, ANONYMOUS, CALLBACKS, ki, JAGAH, NAMED, FUNCTIONS, ALAG, se, DEFINE, karके, CALLBACK, HELL, ko, KAAFI, HAD, TAK, READABLE, banaya, ja, sakta hai — LEKIN, Promises/async-await, EK, CLEANER, MODERN, SOLUTION, HAIN.