10 useful methods of javascript

Sajjad amin
2 min readMay 5, 2021


JavaScript is often derided as a toy language. But after releasing ES6 it becomes more powerful. Nowadays, It is being widely used in every field of modern technology. From server-side to client, It is very popular with web developers. JavaScript has some awesome built-in functions. today I will discuss ten functions of them

  1. Number.isNaN

We know NaN is the special data type of javascript. When we calculate two numbers if one of them is not a valid number, then the calculation result returns NaN. In this situation, we can check if the result valid number or not.

console.log(isNaN(‘a’*10)) // true

2. Number.parseInt

Sometimes, we need to parse numbers from strings. Also, we can convert from various base numbers by using this method.

console.log(Number.parseInt('10', 2)) // 2
//10 is a binary form of 2

3. String.includes

It returns if the string contains the provided value. Remember that, this method is case sensitive.

const str = 'I love Bangladesh'
console.log(str.contains('Bangla')) // true
console.log(str.contains('bangla')) // false

4. String.replace

It replaces the first matched part of the string with the given input.

const str = 'Hello World'
console.log(str.replace('World', 'Earth')) // Hello Earth

5. String.replaceAll

It replaces all matched parts of the string with the given input.

const str = 'We are two brothers and two sisters'
console.log(str.replaceAll('two', 'three'))
// We are three brothers and three sisters

6. String.toLowerCase

It converts all characters of a string to lowercase.

const name = 'Bill Gates'
console.log(name.toLowerCase()) // bill gates

7. String.toUpperCase

It converts all characters of a string to uppercase.

const name = 'Melinda Gates'
console.log(name.toUpperCase()) // MELINDA GATES

8. String.trim

This method removes white space from a string.

const str = '    I love Bangladesh    '
console.log(str.trim()) // 'I love Bangladesh'

9. String.slice

It returns a section of a string by the given index number without modifying the original string

const str = 'I love Bangladesh'
console.log(str.slice(7)) // Bangladesh

10. String.split

It divides a string into an ordered list of substrings according to the given first parameter, puts these substrings into an array, and returns the array.

const str = 'I love Bangladesh'
console.log(str.split(' ')) // ['I', 'love', 'Bangladesh']

That’s all for today, Thanks for reading.



Sajjad amin

I am Sajjad Amin. A passionate programmer. I always like to learn new technology.