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August 31, 2024 17:16
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| // Variable Declarations | |
| let x;// Declares a block-scoped variable | |
| const y = 10; // Declares a block-scoped. read-only constant | |
| // Functions | |
| function myFunction() { | |
| //Function declaration | |
| } | |
| const myFunction = () = { | |
| //Arrow unction exeression | |
| } | |
| // Conditional Statements | |
| if (condition) { | |
| // Executes if condition is true | |
| }else if (otherCondition) { | |
| // Executes if otherCondition is true | |
| } else { | |
| // Executes if all conditions are false | |
| } | |
| // Loops | |
| for (let i = 0; i < 10; i++) { | |
| // For loop; repeats code while a condition is true | |
| } | |
| while (condition) { | |
| // While loop; repeats code while condition is true | |
| } | |
| do { | |
| //Executes code block at least once, then repeats while condition is true | |
| } while (condition); | |
| // Array Methods | |
| let arr = [1, 2, 3]; | |
| arr.push(4); // Adds an element to the end of the array | |
| arr.pop(); // Removes the last element from the array | |
| arr.shift(); // Removes the first element from the array | |
| arr.unshift(0); // Adds an element to the beginning of the array | |
| // Object Methods | |
| let obj = { name: 'John', age: 30 }; | |
| Object.keys(obj);// Returns an array of the object's keys | |
| Object.values(obj ); // Returns an array of the object's values | |
| Object.entries(obj); // Returns an array of the object's key-value pairs | |
| // String Methods | |
| let str = "Hello, world!"; | |
| str.length; // Returns the length of the string | |
| str.toUpperCase(); // Converts string to uppercase | |
| str.toLowerCase(); // Converts string to lowercase | |
| str.includes("world"); // Checks if the string contains "world" | |
| //DOM Manipulation | |
| document.getElementById('id'); // Selects an element by its ID | |
| document.querySelector('.class'); // Selects the first element that matches the CSS selector | |
| document.querySelectorAll( 'div'); // Selects all elements that match the CSS selector | |
| document.createElement('div'); //creates a new HTML element | |
| // Event Listeners | |
| element.addEventListener ('click', function); // Attaches a click event listener to an element | |
| //JSON Methods | |
| JSON.stringify(obj); // Converts a JavaScript object to a JSON string | |
| JSON.parse(jsonStr); // Parses a JSON string into a JavaScript object | |
| // Asynchronous Operations | |
| fetch(url) | |
| .then response = response.json()) // Performs a network request and returns a promise | |
| •then(data = console.log(data)) | |
| •catch(error = console.error(error)); // Catches errors in the fetch process | |
| async function fetchData(){ | |
| // Declares an asynchronous function | |
| try { | |
| let response = await fetch(url): // Waits for the fetch to complete | |
| let data = await response.json(); // Waits for the response to be parsed | |
| console. log(data); // Logs the data | |
| } catch (error) { | |
| console.error(error); // Catches and logs any errors | |
| } | |
| } | |
| // Date and Time | |
| let now = new Date(); // Creates a new date object representing the current date and | |
| now.getFullYear(); // Gets the four-digit year | |
| now.getMonth(); // Gets the month (0-11, January is 0) | |
| now.getDate(); // Gets the day of the month (1-31) | |
| now.getHours(); // Gets the hour (0-23) | |
| now.getMinutes(); // Gets the minutes(0-59) | |
| now.getSeconds(); // Gets the seconds (0-59) | |
| // Error Handling | |
| try { | |
| //Attempts to execute code that may throw an error | |
| } catch (error) { | |
| // Handles the error | |
| console.error(error); // Logs the error to the console | |
| } finally { | |
| // Executes code after try and catch, regardless of the result | |
| } | |
| // Module Imports and Exports | |
| export const myFunction = () => {/* ... */}; // Exports a function from a module | |
| import { myFunction} from './myModule'; // Imports a function from a module | |
| // JavaScript Class | |
| class Person { | |
| constructor(name, age) { // Constructor method for initializing an object | |
| this. name = name; | |
| this.age = age; | |
| } | |
| greet() { | |
| // Method to greet | |
| console. log(`Hello, my name is ${this.name}`); | |
| } | |
| } |
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