| Topic | Description |
|---|---|
| Interview Prep on JS Functions | |
| 1. What is Function Declaration/Definition? | Basic method of creating a function. |
| 2. What is function expression | In JavaScript, a function expression is a way to define a function as a variable. |
| 3. What is anonymous function? | Regular function has 2 parts name and a body, But in JavaScript, you can define a function without a name. You can’t use this, super, or new in an anonymous function. |
| 4. What are First class functions? | First class functions are the functions which can be treated like a variable.This allows for powerful patterns like higher-order functions and callbacks. |
| 5.What is IIFE? | IIFE stands for Immediately Invoked Function Expression. It's a JavaScript design pattern that creates a function expression and immediately executes it. |
| 6.why let is prefered in for loop js? | let is block scope so it can be accessed within the loop only, var is function scoped so it can be accessed outside the loop also which can lead to unwanted bugs. |
| 7. Params vs arguments | The values which we used in function declaration are called Parameters and the values which we provide while calling function is called arguments. |
| 8. What is Callback in JavaScript? | A callback is a JavaScript function passed to another function as an argument, or parameter. This function is executed when the function that it is passed to gets executed. |
| 9.What is the difference between function and method? | - The major difference between methods and functions in JavaScript is that methods are called on objects while functions are not. - Method accepts arguments through an object parameter, and function accepts arguments through a parenthesis parameter. |
| 10. What is the use of void(0) in JavaScript? | void(0) is a special keyword in JavaScript that's used to declare a function that doesn't return any value. When you use void(0), it tells the interpreter that this function should not return anything. |
| 11. What is an arrow function? Give an example. | Arrow function is a shorter way of writing a function, which makes code easier to read/write. |
| 12. What are closures? | A closure is a function that has access to variables in its parent scope(lexical scopin), even after the parent function has finished executing. |
| 13. What are higher order functions? | Higher order are functions that either accept one or more functions as arguments or returns a function. |
Basic method of creating a function.
function sum(a,b){
return a+b;
}In JavaScript, a function expression is a way to define a function as a variable.
const sum = function(a,b){
return a+b;
}Regular function has 2 parts name and a body, But in JavaScript, you can define a function without a name. You can’t use this, super, or new in an anonymous function.
Anonymous functions are functions that don't have a name. it can be accessed by a variable it is stored in.
const sum = function(a,b){
return a+b;
}
const add = (x, y) => x + y;
sum(2,3);Use cases: They are frequently used as callbacks, event handlers, and in higher-order functions.
First class functions are the functions which can be treated like a variable.This allows for powerful patterns like higher-order functions and callbacks.
Functions can be passed as arguments to other functions, enabling powerful patterns like callback functions.
function calculate(x, y, operation) {
return operation(x, y);
}
function add(a, b) {
return a + b;
}
console.log(calculate(5, 3, add)); // Output: 8Functions can be the result of another function, allowing for the creation of higher-order functions.
function createMultiplier(factor) {
return function(x) {
return x * factor;
};
}
const double = createMultiplier(2);
console.log(double(5)); // Output: 10IIFE stands for Immediately Invoked Function Expression. It's a JavaScript design pattern that creates a function expression and immediately executes it.
(function(a,b) {
console.log(a*b);
})(2,3); //output: 6let is block scope so it can be accessed within the loop only, var is function scoped so it can be accessed outside the loop also which can lead to unwanted bugs.
In a for loop, let creates a new variable for each iteration, preventing issues with closures.
With var, only one variable is created for the entire loop, potentially leading to unexpected results when referencing the variable in asynchronous callbacks.
for (let i = 0; i < 5; i++) {
setTimeout(() => console.log(i), 1000);
}
// Output: 0 1 2 3 4
for (var i = 0; i < 5; i++) {
setTimeout(() => console.log(i), 1000);
}
// Output: 5 5 5 5 5 The values which we used in function declaration are called Parameters and the values which we provide while calling function is called arguments.
const sum = function(a,b){ // a,b are Parameters
return a+b;
}
sum(2,3); //2,3 are argumentsA callback is a JavaScript function passed to another function as an argument, or parameter. This function is executed when the function that it is passed to gets executed.
function greet(name, callback) {
console.log(`Hello, ${name}!`);
callback();
}
function sayGoodbye() {
console.log("Goodbye!");
}
greet("John", sayGoodbye);//sayGoodbye is callback function- The major difference between methods and functions in JavaScript is that methods are called on objects while functions are not.
- Method accepts arguments through an object parameter, and function accepts arguments through a parenthesis parameter.
let person = {
name: "Alice",
greet: function() {
console.log("Hello, my name is " + this.name);
}
};
person.greet(); // Output: Hello, my name is Alicevoid(0) is a special keyword in JavaScript that's used to declare a function that doesn't return any value. When you use void(0), it tells the interpreter that this function should not return anything.
<a href="javascript: void(0)">Link</a>When you don't want a link to navigate to another page or reload a page. You can use javascript: void(0) to run code that doesn't change the current page.
const result = void(1 + 1);
console.log(result);
// undefined1 + 1 is evaluated but undefined is returned.
Arrow function is a shorter way of writing a function, which makes code easier to read/write.
Arrow functions implicitly bind the this keyword to the enclosing scope, so you don't need to use bind(), call(), or apply() to bind it to the current object.
let myFunction = (a, b) => a * b;
console.log(myFunction(5,10) //50For example, arrow functions can help you write code that is easier to read and understand when you need to write several small functions for event listeners.
document.getElementById("btn").addEventListener("click", () => {
document.getElementById("demo").innerHTML += this;
});A closure is a function that has access to variables in its parent scope(lexical scopin), even after the parent function has finished executing.
JavaScript uses lexical scoping, meaning a variable's scope is determined by its position in the source code. Inner functions have access to variables in their outer functions.
function outerFunction() {
let count = 0;
function innerFunction() { //closure
count++;
console.log(count);
}
return innerFunction;
}
let counter = outerFunction();
counter(); // Outputs: 1
counter(); // Outputs: 2Higher order are functions that either accept one or more functions as arguments or returns a function.
// Callback function, passed as a parameter in the higher order function
function callbackFunction(){
console.log('I am a callback function');
}
// higher order function
function higherOrderFunction(func){
console.log('I am higher order function')
func()
}
higherOrderFunction(callbackFunction); When working with arrays, you can use the map(), reduce(), filter(), and sort() functions to manipulate and transform data in an array.