JavaScript, as a dynamically-typed language, provides two distinct primitive values to represent the absence of a meaningful value: undefined and null. Although they might seem similar at first glance, they have different meanings and behaviors. Understanding the difference between undefined and null is crucial for writing clean and bug-free JavaScript
Ruby, a dynamic, object-oriented programming language, offers several methods for outputting information to the console. Among the commonly used ones are puts, print, and p. While they might seem similar at first glance, each serves a distinct purpose in Ruby programming. Let’s delve into each of these methods to understand
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Python is a versatile, high-level programming language that is widely used for web development, data analysis, machine learning, and artificial intelligence. It is known for its simplicity, readability, and ease of use. If you're new to programming or just getting started with Python, this article will cover the fundamentals that you need to know.
Variables are used to store data in JavaScript. They can be declared using the "let", "const", or "var" keywords. The "let" keyword is used to declare variables that can be changed, while "const" is used to declare constants that cannot be changed. The "var" keyword is an older way of declaring variables and has some differences in scope compared to "let" and "const".
Here is an example of declaring and using variables:
let firstName = 'John';
const PI = 3.14;
var age = 30;
console.log(firstName); // Output: Johnconsole.log(PI); // Output: 3.14console.log(age); // Output: 30
firstName = 'Jane';
console.log(firstName); // Output: Jane// PI = 3.1415; // This will throw an error since PI is a constant
JavaScript has several built-in data types, including strings, numbers, booleans, null, and undefined.
let name = 'John';
let age = 30;
let isMarried = false;
let car = null;
let job; // undefinedconsole.log(typeof name); // Output: stringconsole.log(typeof age); // Output: numberconsole.log(typeof isMarried); // Output: booleanconsole.log(typeof car); // Output: objectconsole.log(typeof job); // Output: undefined
Control flow is used to control the order in which code is executed. The most common control flow structures in JavaScript are conditional statements and loops.
Conditional statements are used to execute code based on a condition. The most common conditional statements in JavaScript are "if", "else if", and "else".
let age = 18;
if (age >= 18) {
console.log('You can vote');
} else {
console.log('You cannot vote');
}
Loops are used to execute code repeatedly. The most common loops in JavaScript are "for", "while", and "do while".
function sum(a, b) {
return a + b;
}
console.log(sum(1, 2)); // Output: 3
Here is an example of a function that takes two parameters and returns their sum:
function sum(a, b) {
return a + b;
}
console.log(sum(1, 2)); // Output: 3
Functions can also be assigned to variables, passed as arguments to other functions, and returned from functions.
Objects are used to store data and functions together in a single container. They are defined using curly braces {} and can contain properties and methods.
Here is an example of defining an object and accessing its properties:
let person = {
firstName: 'John',
lastName: 'Doe',
age: 30,
getFullName: function() {
return this.firstName + ' ' + this.lastName;
}
};
console.log(person.firstName); // Output: Johnconsole
console.log(person.getFullName()); // Output: John Doe
Objects can also be nested inside other objects and can be created using constructor functions and classes.
Arrays are used to store multiple values in a single variable. They are defined using square brackets [] and can contain any type of data.
Here is an example of creating an array and accessing its elements:
let numbers = [1, 2, 3, 4, 5];
console.log(numbers[0]); // Output: 1
console.log(numbers.length); // Output: 5
Arrays also have built-in methods, such as "push", "pop", "shift", and "unshift", that allow elements to be added or removed from the array.
let fruits = ['apple', 'banana'];
fruits.push('orange');
console.log(fruits); // Output: ['apple', 'banana', 'orange']
fruits.pop();
console.log(fruits); // Output: ['apple', 'banana']
In conclusion, JavaScript is a powerful and flexible programming language that is widely used for web development. This article has covered the fundamental concepts of JavaScript, including variables, data types, control flow, functions, objects, and arrays. With this knowledge, beginners can start exploring the vast ecosystem of JavaScript libraries and frameworks to build dynamic and interactive web applications.
For the purpose of this example, let's assume that the API we're interacting with has the following endpoints: - GET /articles: Returns a list of all articles in the API. - POST /articles: Creates a new article. - PUT /articles/:id: Updates an article with a specific ID. - GET /articles/:id: Retrieves an article with a specific ID. To interact with this API, we'll be using the fetch function provided by modern web browsers. This function allows us to make HTTP requests to external APIs and handle the responses in a convenient way. First, let's start by creating a module that will handle our API interactions. We'll create a file called api.js and export an object with four methods: getArticles, createArticle, updateArticle, and getArticle.
const API_BASE_URL = 'https://example.com/api';
const api = {
async getArticles() {
const response = await fetch(`${API_BASE_URL}/articles`);
const data = await response.json();
return data;
},
async createArticle(article) {
const response = await fetch(`${API_BASE_URL}/articles`, {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(article),
});
const data = await response.json();
return data;
},
async updateArticle(id, article) {
const response = await fetch(`${API_BASE_URL}/articles/${id}`, {
method: 'PUT',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(article),
});
const data = await response.json();
return data;
},
async getArticle(id) {
const response = await fetch(`${API_BASE_URL}/articles/${id}`);
const data = await response.json();
return data;
},
};
export default api;
Now that we have our API module, we can create a simple user interface that allows us to interact with it. For the purpose of this example, we'll create a form that allows us to create new articles, and a table that displays all existing articles and allows us to update and delete them.
We'll create a file called app.js and include it in an HTML file with the following structure:
<!--
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title> Articles </title></head><body><h2>Articles</h2><form id="create-article-form"><label for="title">Title:</label><input type="text" id="title" name="title" required><br><label for="content">Content:</label><textarea id="content" name="content" required></textarea><br><button type="submit">Create</button></form><table id="articles-table"><thead><tr><th>ID</th><th>Title</th><th>Content</th><th>Actions</th></tr></thead><tbody></tbody></table><script type="module" src="app.js"></script></body></html> -->
This HTML file includes a form with two input fields (title and content) and a submit button, and a table with four columns (ID, Title, Content, and Actions). We've also included a script tag that loads our app.js file as a module.
Now let's write the code for our app.js module. We'll start by importing our api.js module and the HTML elements we'll be working with.
import api from './api. js';
const createArticleForm = document.getElementById('create-article-form');
const articlesTableBody = document.querySelector('#articles-table tbody');
Next, let's create a function that will display all existing articles in our table. We'll call this function displayArticles and we'll use the getArticles method from our API module to fetch the data.
async function displayArticles() {
const articles = await api.getArticles();
articlesTableBody.innerHTML = '';
for (const article of articles) {
const tr = document.createElement('tr');
tr.innerHTML = `
<td>${article.id}</td>
<td>${article.title}</td>
<td>${article.content}</td>
<td>
<button class="edit-article-button" data-article-id="${article.id}">Edit</button>
<button class="delete-article-button" data-article-id="${article.id}">Delete</button>
</td>
`;
articlesTableBody.appendChild(tr);
}
}
This function first calls getArticles and awaits its response. It then clears the tbody of our table and creates a new tr element for each article, populating its cells with the article's properties (id, title, and content) and adding two buttons (Edit and Delete) with a data-article-id attribute set to the article's ID.
We'll also need a function to handle the submission of our create article form. This function will be called handleCreateArticleFormSubmit and it will use the createArticle method from our API module to send the form data to the API.
createArticleForm.addEventListener('submit', async event => {
event.preventDefault();
const formData = new FormData(event.target);
const title = formData.get('title');
const content = formData.get('content');
await api.createArticle({ title, content });
createArticleForm.reset();
await displayArticles();
});
This function first prevents the default form submission behavior (which would cause a page reload), then creates a FormData object from the form element and extracts the values of the title and content fields. It then calls createArticle with an object containing these values, and awaits the response. Finally, it resets the form and calls displayArticles to update the table.
Next, we'll create a function to handle the click event on our Edit buttons. This function will be called handleEditArticleButtonClick and it will display a form that allows us to update the selected article.
articlesTableBody.addEventListener('click', async event => {
if (event.target.matches('.edit-article-button')) {
const articleId = event.target.dataset.articleId;
const article = await api.getArticle(articleId);
const tr = event.target.closest('tr');
tr.innerHTML = `
<td>${article.id}</td>
<td><input type="text" name="title" value="${article.title}" required></td>
<td><textarea name="content" required>${article.content}</textarea></td>
<td>
<button class="update-article-button" data-article-id="${article.id}">Update</button>
<button class="cancel-update-article-button" data-article-id="${article.id}">Cancel</button>
</td>
`;
This function first checks if the clicked element matches the .edit-article-button selector. If it does, it retrieves the article ID from the data-article-id attribute of the button and calls getArticle to fetch the article data.
It then selects the closest tr element (which represents the row of the clicked button) and replaces its content with a new form that allows us to update the article's title and content. The form includes two buttons (Update and Cancel) with a data-article-id attribute set to the article's ID.
We'll need another function to handle the submission of the update form. This function will be called handleUpdateArticleFormSubmit and it will use the updateArticle method from our API module to send the updated article data to the API.
articlesTableBody.addEventListener('click', async event => {
if (event.target.matches('.update-article-button')) {
const formData = new FormData(event.target.closest('tr'));
const title = formData.get('title');
const content = formData.get('content');
const articleId = event.target.dataset.articleId;
await api.updateArticle(articleId, { title, content });
await displayArticles();
}
});
This function first retrieves the form data from the closest tr element of the clicked button, extracts the values of the title and content fields, and retrieves the article ID from the data-article-id attribute of the button.
It then calls updateArticle with the article ID and an object containing the updated title and content, and awaits the response. Finally, it calls displayArticles to update the table.
We'll also need a function to handle the click event on our Cancel buttons. This function will be called handleCancelUpdateArticleButtonClick and it will cancel the update and restore the original article data.
articlesTableBody.addEventListener('click', async event => {
if (event.target.matches('.cancel-update-article-button')) {
const articleId = event.target.dataset.articleId;
const article = await api.getArticle(articleId);
const tr = event.target.closest('tr');
tr.innerHTML = `
<td>${article.id}</td>
<td>${article.title}</td>
<td>${article.content}</td>
<td>
<button class="edit-article-button" data-article-id="${article.id}">Edit</button>
<button class="delete-article-button" data-article-id="${article.id}">Delete</button>
</td>
`;
}
});
This function retrieves the article ID from the data-article-id attribute of the clicked button and calls getArticle to fetch the original article data.
It then selects the closest tr element (which represents the row of the clicked button) and replaces its content with the original article data, including the Edit and Delete buttons.
Finally, we'll create a function to handle the click event on our Delete buttons. This function will be called handleDeleteArticleButtonClick and it will use the deleteArticle method from our API module to delete the selected article.
articlesTableBody.addEventListener('click', async event => {
if (event.target.matches('.delete-article-button')) {
const articleId = event.target.dataset.articleId;
await api.deleteArticle(articleId);
await displayArticles();
}
});
This function retrieves the article ID from the data-article-id attribute of the clicked button and calls deleteArticle with this ID. It then awaits the response and calls displayArticles to update the table.
And that's it! We now have a complete JavaScript application
