Array Methods in JavaScript
Here’s a list of commonly used array methods with brief explanations and practical interview questions.
Common Array Methods:
push(): Adds elements to the end of the array.
pop(): Removes the last element from the array.
unshift(): Adds elements to the beginning of the array.
shift(): Removes the first element from the array.
map(): Creates a new array by applying a function to each element.
filter(): Creates a new array with elements that pass the test provided by a function.
reduce(): Reduces the array to a single value based on a reducer function.
forEach(): Iterates through each element in the array without returning a value.
find(): Returns the first element that satisfies the provided testing function.
findIndex(): Returns the index of the first element that satisfies the provided testing function.
includes(): Checks if an array contains a certain value.
indexOf(): Returns the index of the first occurrence of a value.
slice(): Returns a shallow copy of a portion of the array.
splice(): Adds/removes elements from the array at specified positions.
concat(): Merges two or more arrays into a new array.
join(): Joins all elements of an array into a string.
reverse(): Reverses the order of the array elements.
sort(): Sorts the array in place.
Array Practical Interview Questions:
Using filter and map: Question: Write a function that takes an array of numbers and returns an array of squares of even numbers.
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const numbers = [1, 2, 3, 4, 5, 6];
const evenSquares = numbers.filter(num => num % 2 === 0).map(num => num * num);
console.log(evenSquares); // Output: [4, 16, 36]
Using reduce: Question: Write a function to calculate the sum of all elements in an array.
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const numbers = [1, 2, 3, 4];
const sum = numbers.reduce((acc, curr) => acc + curr, 0);
console.log(sum); // Output: 10
Using find: Question: Find the first number in the array greater than 10.
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const numbers = [4, 9, 15, 2];
const firstGreater = numbers.find(num => num > 10);
console.log(firstGreater); // Output: 15
Using splice: Question: Remove the 3rd element from the array.
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const array = [1, 2, 3, 4, 5];
array.splice(2, 1); // Removes the element at index 2
console.log(array); // Output: [1, 2, 4, 5]
Object Methods in JavaScript
Common Object Methods:
Object.keys(obj): Returns an array of an object's keys.
Object.values(obj): Returns an array of an object's values.
Object.entries(obj): Returns an array of key-value pairs.
Object.assign(target, ...sources): Copies properties from one or more source objects to a target object.
Object.freeze(obj): Freezes an object, preventing additions or modifications.
Object.seal(obj): Seals an object, allowing modifications of existing properties but preventing new properties.
Object.create(proto): Creates a new object with the specified prototype.
Object.is(value1, value2): Compares two values for equality.
Object.fromEntries(entries): Converts key-value pairs into an object.
Object.hasOwnProperty(key): Checks if an object has the specified key as a direct property.
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