Here are a few more commonly asked Javascript Interview questions and their answers:
JavaScript is a programming language that is primarily used for creating interactive web pages and web applications. It runs in a web browser and is supported by all major web browsers.
JavaScript and Java are two different programming languages that have similar names but are not related. Java is a general-purpose programming language that can be used for building a variety of applications, while JavaScript is a programming language that is primarily used for creating web applications.
You can declare a variable in JavaScript using the var, let, or const keyword. For example:
var x = 10;
let y = "Hello";
const z = true;Recommended post: Javascript ES6 Interview Questions and Answers
The data types in JavaScript are: string, number, boolean, undefined, null, object, and symbol.
The different types of operators in JavaScript are: arithmetic, assignment, comparison, logical, bitwise, and ternary operators.
You can create an object in JavaScript using object literal notation or constructor functions. For example:
// Using object literal notation
var person = { name: "John", age: 30 };
// Using constructor functions
function Person(name, age) {
this.name = name;
this.age = age;
}
var person = new Person("John", 30);In JavaScript, null is an explicitly assigned value that represents the absence of any object value, while undefined is a value assigned by the system to variables that have not been assigned a value.
The double equal (==) operator in JavaScript checks for equality between two values, but performs type coercion if the values are of different types. The triple equal (===) operator checks for both equality and type equality between two values.
You can handle errors in JavaScript using try…catch statements. For example:
try {
// Code that might throw an error
} catch (error) {
// Code that handles the error
}You can use the console.log() method to output messages to the browser console, use breakpoints in the browser developer tools, and use the debugger statement to pause execution of the code.
You can work with arrays in JavaScript using methods such as push(), pop(), shift(), unshift(), splice(), slice(), and forEach().
You can loop through objects in JavaScript using a for…in loop. For example:
var person = { name: "John", age: 30 };
for (var key in person) {
console.log(key + ": " + person[key]);
}You can use if/else statements in JavaScript to control the flow of your code based on certain conditions. For example:
if (x > 10) {
// Code to execute if x is greater than 10
} else {
// Code to execute if x is less than or equal to 10
}You can define functions in JavaScript using the function keyword. For example:
function add(x, y) {
return x + y;
}
var result = add(3, 5);You can use callbacks in JavaScript by passing a function as an argument to another function, which will then call the function at a later time. For example:
function doSomething(callback) {
// Code to do something
callback();
}
function sayHello() {
console.log("Hello!");
}
doSomething(sayHello);Synchronous programming is when code is executed in a linear fashion, one statement at a time, while asynchronous programming allows code to be executed out of order, with non-blocking functions that can be executed independently.
Promises in JavaScript allow you to handle asynchronous code in a more organized way. You can create a new Promise using the Promise constructor and then use the .then() and .catch() methods to handle the resolved or rejected state of the Promise. For example:
function getData() {
return new Promise(function(resolve, reject) {
// Code to get data
if (data) {
resolve(data);
} else {
reject("Error: Data not found");
}
});
}
getData().then(function(data) {
console.log(data);
}).catch(function(error) {
console.log(error);
});The event loop is a mechanism in JavaScript that allows for non-blocking I/O operations by continuously checking the call stack and the message queue for new events to process.
You can work with the Document Object Model (DOM) in JavaScript to manipulate the structure and content of a web page. You can use methods such as getElementById(), getElementsByClassName(), and querySelector() to select elements on the page, and then use properties such as innerHTML, className, and style to modify the elements.
You can handle user input in JavaScript using event listeners, which allow you to execute code in response to a user action such as a button click or a key press. For example:
var button = document.getElementById("myButton");
button.addEventListener("click", function() {
// Code to execute when button is clicked
});In JavaScript, null is a value that represents the intentional absence of any object value, while undefined represents a variable or object that has not been assigned a value.
Hoisting is a mechanism in JavaScript where variable and function declarations are moved to the top of their respective scopes, allowing them to be used before they are declared. This behavior can sometimes lead to unexpected results, so it’s important to be aware of it when writing JavaScript code.
The “this” keyword in JavaScript refers to the object that the function is a method of. In other words, “this” refers to the object that the function is being called on. If a function is not called as a method of an object, “this” will refer to the global object.
“==” is a loose comparison operator in JavaScript that compares two values for equality after converting their types, while “===” is a strict comparison operator that compares two values for equality without converting their types.
You can declare a variable in JavaScript using the “var”, “let”, or “const” keywords. For example:
var myVariable = 10;
let myOtherVariable = "Hello, world!";
const myConstant = [1, 2, 3];A closure in JavaScript is a function that has access to the variables and parameters of its outer function, even after the outer function has returned. Closures are often used to create private variables and functions in JavaScript.
Arrow functions are a shorthand syntax for creating functions in JavaScript that have a more concise syntax and a different “this” binding behavior than regular functions. Arrow functions are more suitable for writing small, one-liner functions, while regular functions are better for more complex functions with more advanced functionality.
You can create an object in JavaScript using either the object literal syntax or the constructor syntax. For example:
// Object literal syntax
var myObject = {
name: "John",
age: 30
};
// Constructor syntax
function Person(name, age) {
this.name = name;
this.age = age;
}
var myPerson = new Person("John", 30);A for loop is a more general-purpose loop in JavaScript that can be used to loop through any iterable object, while a forEach loop is specifically designed to loop through the elements of an array. The forEach loop also has a callback function that is executed for each element of the array.
A module in JavaScript is a way to organize and encapsulate code into self-contained units of functionality that can be imported and used in other parts of an application. Modules can be created using the “export” and “import” keywords.
A constructor function in JavaScript is a special type of function that is used to create new objects with a specific set of properties and methods. Constructor functions use the “this” keyword to set properties and methods on the new object, and can be called using the “new” keyword.
Callback hell is a situation that can occur in JavaScript code when multiple levels of nested callbacks are used, leading to code that is difficult to read, understand, and maintain. This can be mitigated by using promises or async/await syntax.
A shallow copy in JavaScript creates a new object or array that contains references to the same values as the original object or array, while a deep copy creates a new object or array with new copies of all the values. Shallow copying can be done using the spread operator or Object.assign(), while deep copying can be done using various techniques such as JSON.parse(JSON.stringify()) or recursion.
Event bubbling is a mechanism in JavaScript where when an event is triggered on a child element, the event will also propagate up the DOM tree and trigger any event listeners on parent elements as well. This behavior can be controlled using the stopPropagation() method.
I hope these answers are helpful! Let me know if you have any more questions.
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