What is Closures in JavaScript?
Closures are a powerful and important concept in JavaScript, but they can be difficult to understand. In simple terms, a closure is a function that has access to variables in its outer function, even after the outer function has returned.
Here in detail about it Closures in JavaScript.
Here's an example to illustrate the concept of closures:
function outerFunction() {
let count = 0;
return function innerFunction() {
count++;
console.log(count);
}
}
const inner = outerFunction();
inner(); // output: 1
inner(); // output: 2
In the above code, outerFunction() creates a variable count and returns an inner function innerFunction. When innerFunction is executed, it has access to the count variable, indeed though outerFunction has formerly returned. This is possible because of closures.
Then are a many effects to keep in mind about closures
Closures have access to variables in their external function's compass, indeed after the external function has returned.
Closures capture the variables they need to pierce. This means that if a check uses a variable from its external function, that variable won't be scrap collected indeed if the external function has finished executing.
Closures can be used to produce private variables and styles. By creating a check, you can hide certain variables and styles from the global compass, precluding them from being penetrated or modified by other corridor of your law.
Closures can be created with anonymous functions or with named functions.
In Simpal words, closures allow you to produce functions that have access to variables in their external function's compass, indeed after the external function has returned. They're a important tool in JavaScript and can be used to produce private variables and styles, among other effects.
What is the use of Closures in JavaScript.
The JavaScript idea of closures is crucial because it enables functions to keep track of and access variables from the parent scope even after the parent function has finished running. To put it another way, a closure is a function that has access to variables in the scope of the function that it is enclosing.
Closures in JavaScript are mostly used to define private variables and functions. A private variable or function is one that is only available from within the enclosing function and any nested functions; it is not accessible from the outside.
Consider the following example:
function counter() {
let count = 0;
return function() {
count++;
console.log(count);
}
}
const increment = counter();
increment(); // 1
increment(); // 2
increment(); // 3
In this example, we define a function counter() that returns an anonymous function. The anonymous function has access to the count variable in the counter() function, even though counter() has already returned. This is possible because the anonymous function forms a closure over the count variable.
We then call counter() and assign the returned function to the increment variable. We can then call increment() multiple times, and each time it will log the next number in the count sequence.
Another use of closures is in event handling. When we add an event listener to an element in the DOM, we often want the event handler to have access to certain variables in our code. Closures allow us to do this by creating a function that forms a closure over the necessary variables, and then passing that function as the event handler.
What is Promises in JavaScript?
An essential idea in JavaScript is the promise, which is used to manage asynchronous processes. An asynchronous operation's eventual success (or failure) and the value it produces are represented as promises.
Here in detail about it Promises in JavaScript.
Here's an example to illustrate how promises work:
const promise = new Promise((resolve, reject) => {
// Some async operation
setTimeout(() => {
resolve('Success!');
}, 1000);
});
promise.then((result) => {
console.log(result); // Output: Success!
});
In the code above, we create a new promise using the Promise constructor. The constructor takes a function with two parameters: resolve and reject. Inside this function, we perform some async operation and then call resolve with the resulting value.
We then attach a then method to the promise, which takes a function that will be called when the promise is resolved. In this case, the function simply logs the resulting value to the console.
Promises can also be used to handle errors:
const promise = new Promise((resolve, reject) => {
// Some async operation
setTimeout(() => {
reject('Error!');
}, 1000);
});
promise.catch((error) => {
console.error(error); // Output: Error!
});
In this code, we reject the promise with an error message. We then attach a catch method to the promise, which takes a function that will be called when the promise is rejected.
Here are a few things to keep in mind about promises:
- Promises have three states: pending, fulfilled, and rejected.
- Promises are chainable. This means that you can attach multiple then and catch methods to a single promise.
- Promises can be used to handle multiple async operations in parallel.
- Promises can be created using the Promise constructor or by using a library that provides a promise-based API.
In other words, promises are a powerful tool for handling asynchronous operations in JavaScript. They allow you to write cleaner and more concise code, and they provide a standard way of handling errors and multiple async operations.