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https://github.com/iamabhaytiwari343/javascript
this repository contains the basic fundamentals of most widely used language of web "javascript"
https://github.com/iamabhaytiwari343/javascript
basic fundamentals javascript programming
Last synced: 4 days ago
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this repository contains the basic fundamentals of most widely used language of web "javascript"
- Host: GitHub
- URL: https://github.com/iamabhaytiwari343/javascript
- Owner: iamabhaytiwari343
- Created: 2023-03-27T05:22:31.000Z (almost 2 years ago)
- Default Branch: master
- Last Pushed: 2023-12-15T17:01:17.000Z (about 1 year ago)
- Last Synced: 2023-12-15T18:23:59.955Z (about 1 year ago)
- Topics: basic, fundamentals, javascript, programming
- Language: JavaScript
- Homepage:
- Size: 152 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# javascript
refer to: https://roadmap.sh/javascript
# Understanding JavaScript Closures
Closures are a fundamental concept in JavaScript that may initially appear complex, but I'll explain them in simple terms with an example to make it more accessible.
## What are Closures?
Imagine you have a function within another function. The inner function has access to the variables and parameters of the outer function, even after the outer function has finished running. This is what we call a closure.
## Example
Let's illustrate closures with a simple example:
```javascript
function outerFunction(x) {
// This is the outer function
return function innerFunction(y) {
// This is the inner function
return x + y;
};
}
const closure = outerFunction(10); // 'closure' now stores the inner function
const result = closure(5); // When we call 'closure', it still remembers 'x'
console.log(result); // Outputs 15
```
# Understanding Anonymous Functions and Arrow Functions in JavaScript
Anonymous functions and arrow functions are two different ways of writing functions in JavaScript. Let's explain them in simple terms with examples.
## Anonymous Function
An anonymous function is a function without a name. It's often used when you need a function for a short task, like passing it as an argument to another function. Here's how it looks:
```javascript
const add = function(x, y) {
return x + y;
};
const result = add(3, 5);
console.log(result); // Outputs 8
```
## Arrow Functions
Arrow functions are a more concise way of writing functions, introduced in ES6 (ECMAScript 2015). They are especially handy for shorter functions. Here's how an arrow function works:
```javascript
const add = (x, y) => x + y;
const result = add(3, 5);
console.log(result); // Outputs 8
```
In this example, the arrow function add is defined using (x, y) => x + y, which is a shorter way of writing a function. It takes two parameters and returns their sum. The result is the same as with the anonymous function.
The key difference between the two is that arrow functions have a shorter syntax and automatically capture the value of this from their surrounding context, which can be beneficial in certain situations. Anonymous functions, on the other hand, are more flexible and allow you to name the function if needed.
# Promises and Their Methods (then, catch, finally)
Promises are a fundamental concept in JavaScript for handling asynchronous operations. They provide a way to work with data or perform actions that may take some time to complete. Promises have three important methods: `then`, `catch`, and `finally`.
## `then`
The `then` method is used to handle the successful completion of a Promise. It takes one or two arguments:
1. A callback function that will be executed when the Promise is resolved (i.e., when the asynchronous operation succeeds).
2. An optional callback function that will be executed when the Promise is rejected (if there's an error).
```javascript
const promise = new Promise((resolve, reject) => {
// Simulate an asynchronous operation
setTimeout(() => {
const data = "Success!";
resolve(data); // Resolve the Promise with the data
}, 1000);
});
promise.then((data) => {
console.log("Resolved:", data); // Output: Resolved: Success!
}).catch((error) => {
console.error("Rejected:", error);
});
```
## catch
The catch method is used to handle errors or rejections of a Promise. It takes a callback function that will be executed when the Promise is rejected. If an error occurs in the Promise, it will jump to the nearest catch block.
```
const promise = new Promise((resolve, reject) => {
setTimeout(() => {
reject("Something went wrong!"); // Reject the Promise with an error message
}, 1000);
});
promise.then((data) => {
console.log("Resolved:", data);
}).catch((error) => {
console.error("Rejected:", error); // Output: Rejected: Something went wrong!
});
```
## finally
The finally method is used to specify a callback function that will be executed regardless of whether the Promise is resolved or rejected. It's useful for cleanup operations that need to be performed in any case.
```
const promise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve("Success!");
}, 1000);
});
promise
.then((data) => {
console.log("Resolved:", data);
})
.catch((error) => {
console.error("Rejected:", error);
})
.finally(() => {
console.log("Promise completed, regardless of outcome.");
});
```
Promises, along with their then, catch, and finally methods, provide a structured way to work with asynchronous operations in JavaScript, making it easier to handle both successful results and errors.
Please let me know if you would like more details on any specific aspect or have additional questions.
### Promise.all and Promise.race
Promise.all and Promise.race are two methods for handling multiple promises in JavaScript. They are useful when you have several asynchronous tasks that need to be coordinated or when you want to deal with the first result among several promises.
#### Promise.all
- Promise.all takes an array of promises as input and returns a new promise.
- This new promise resolves when all the input promises have resolved or rejects as soon as any one of them rejects.
- It returns an array of resolved values corresponding to the input promises in the same order.
```
const promise1 = fetch('https://api.example.com/data1');
const promise2 = fetch('https://api.example.com/data2');
Promise.all([promise1, promise2])
.then((results) => {
console.log('All promises resolved:', results);
})
.catch((error) => {
console.error('At least one promise rejected:', error);
});
```
#### Promise.race
- Promise.race also takes an array of promises as input and returns a new promise.
- This new promise resolves or rejects as soon as the first promise in the input array resolves or rejects. It doesn't wait for all promises to complete.
```
const promise1 = fetch('https://api.example.com/data1');
const promise2 = fetch('https://api.example.com/data2');
Promise.race([promise1, promise2])
.then((result) => {
console.log('The first promise to resolve:', result);
})
.catch((error) => {
console.error('The first promise to reject:', error);
});
```
In the case of Promise.all, you ensure that all promises have completed successfully, and you get an array of their results. In the case of Promise.race, you get the result (or error) of the first promise to resolve or reject. These methods are handy for scenarios where you need to coordinate multiple asynchronous operations.
### Handling Async Operations
Handling asynchronous operations in JavaScript involves working with promises and other asynchronous patterns to ensure that your code doesn't block and remains responsive to other tasks.
#### Using Promises
Promises are a way to manage asynchronous operations in a more structured and readable manner. You can create a promise and specify what should happen when the operation is complete (resolved) or encounters an error (rejected).
```
const fetchData = () => {
return new Promise((resolve, reject) => {
setTimeout(() => {
// Simulate data retrieval
const data = 'Some data';
resolve(data); // Resolve with the data
}, 1000);
});
};
fetchData()
.then((data) => {
console.log('Data received:', data);
})
.catch((error) => {
console.error('Error:', error);
});
```
#### Async/Await
Async/await is a more recent addition to JavaScript that simplifies working with promises. It allows you to write asynchronous code in a more synchronous-like fashion, making it easier to read and maintain.
```
const fetchData = async () => {
try {
const data = await fetch('https://api.example.com/data');
console.log('Data received:', data);
} catch (error) {
console.error('Error:', error);
}
};
fetchData();
```
#### CallBacks
Callbacks are a traditional way to handle asynchronous operations. You pass a function (the callback) that should be executed when the operation is complete. However, this can lead to callback hell or deeply nested functions when dealing with multiple async tasks.
```
const fetchData = (callback) => {
setTimeout(() => {
const data = 'Some data';
callback(data);
}, 1000);
};
fetchData((data) => {
console.log('Data received:', data);
});
```