In this article, we will focus on some of the important JavaScript methods. The sections will be broken down by module.

Javascript String Methods

1. charAt()

const name = "Thor"
console.log(name.charAt(0))
//T

In another way, we also find a specific character in our string. This method is like an array value finding.

const movie = "Thor"
console.log(movie[0])
//T

2. concat()

const fristName = "Jon";
const lastName = "Doe";
console.log(fristName.concat(" ",lastName))

3.includes()

Includes method checks if a specific value exists or not, and it returns a boolean value.

Note: The includes methods are case-sensitive.

const country = "Bangladesh is my Born country"
console.log(country.includes("Bangladesh")) //true
console.log(country.includes("bangladesh")) //false

4. endsWith()

This method helps to check which sentence uses in a substring in the last position.

Note: The endsWith method is also case-sensitive.

const dialog = "I will must tech you who am i?"
console.log(dialog.endsWith("i?")) //true
console.log(dialog.endsWith("i")) //false

5.indexOf()

This indexOf method searches for a specified value, and if a value exists then, return values position index, otherwise return -1 value if not found.

const para = 'The quick brown fox';
console.log(para.indexOf('quick')) //4
console.log(para.indexOf('Jump')) //-1

6.lastIndexOf()

The lastIndexOf() method returns the position of the last occurrence of a specified value in a string.

Note: The lastIndexOf method also is case-sensitive.

const list = ["Mango", "Apple", "Mango"];
list.lastIndexOf("Mango"); //2

7.replace()

The replace method replaces characters in a string with another group of characters.

const grettings = "Welcome to Dhaka";
grettings.replace("Dhaka","Noakkhali")
//"Welcome to Noakkhali"

8.splice()

This method returns a new substring based on the indexes provided.

const sing = "I am a disco dancer"
console.log(sing.slice(0,5))// I am

9.split()

Using substrings to split a string into an array. It returns the new array.

const ask = "How are you?"
const res = ask.split(" ") //["How", "are", "you?"]

10.startsWith()

This method returns the boolean value if the string begins with a substring.

const myName = "I am Jobayer Hossain"
myName.startsWith("I")//true
myName.startsWith("am")//false

11.substr()

This method accepts two input values as the number and extracts a string with a beginning number to end several target string positions.

const helloMsg = "Hello How are you?"
const res = helloMsg.substr(1,4) //"ello"

12.toLowerCase()

It converts a string to lower case.

const str1 = "Hellow World"
const str1Res = str1.toLowerCase()//"hellow world"

Note: The toLowerCase() the function doesn't accept any parameters. and does not changers the original string.

13.toUpperCase()

The method transforms a string to uppercase letters.

const str2 = "Hellow World"
const str2Res = str2.toUpperCase() //"HELLOW WORLD"

Note: The toUpperCase() method does not modify the original string.

14.trim()

The trim()the method removes all whitespace on the string at the beginning and ending positions.

const str3 = "   Hellow   World! "
const str3Res = str3.trim() //"Hellow   World!"

Note: The trim() method does not modify the initial string, and it does not accept any parameters.

15.trimStart()

This method removes whitespace only from the start.

const str4 = "       Hello World!     ";
const str4Res = str4.trimStart() // "Hello World!     "

16.trimEnd()

This method removes whitespace only from the end.

const str5 = "    HelloWorld    ";
const str5Res = str5.trimEnd() // "    HelloWorld"

Javascript Number Methods

1.isNaN()

This method returns true if the value is not a number.

console.log(isNaN(123)) // false
console.log(isNaN(true)) // false
console.log(isNaN(true)) // falseconsole.log(isNaN("Hello")) // true
console.log(isNaN("2020/4/13")) // true
console.log(isNaN(undefined)) // true
console.log(isNaN(NaN)) // true

2.parseFloat()

The function parses a string and returns a floating-point number.

console.log(parseFloat("40")) //40
console.log(parseFloat(" 50.55  ")) //50.55
console.log(parseFloat("My ID 40")) //NaN

3.parseInt()

This function parses a string and delivers an integer.

console.log(parseInt("10")) //10
console.log(parseInt("  30.90")) //30
console.log(parseInt("36 10 20")) //36
console.log(parseInt("ID 404")) // NaN

JavaScript Array methods

1.concat()

The concat function is used to join two arrays and returns a new array.

const marvelHeros =  ["Thor","Ant-man"]
const dcHeros = ["WonderWoman","Bat Man"]
const joniArrays = marvelHeros.concat(dcHeros)
//["Thor","Ant-man", "WonderWoman","Bat Man"]

2.every()

This method tests if all elements in an array pass a test.

const agesArray = [32,42,53]
const hasAudlt = agesArray.every(age=> age < 18) //false

3.filter()

This method generates a new array with all array elements that pass a condition.

const numberArrays = [5,9,12,22,53]
const filterdLessThen20 = numberArrays.filter(num => num < 20) 
//[5, 9, 12]

4.find()

This function returns the value of the array that passes a condition.

const districts = ["comilla","Noakhalli","Lakshimipur"]
const myDistrict = districts.find((district) => {
     return district == "Lakshimipur"
})
//"Lakshimipur"

5.findIndex()

This method returns the index of the first item that passes a test.

const array1 = [5, 12, 8, 230, 44];
const lessThen15 = array1.findIndex(num => num > 15) //3

6.forEach()

forEach method work looks like a for loop. It loops through all the elements in the array and returns a single piece of the element.

const friendsArray = ["Jon", "Doyt", "cherry"];
const friendsName = friendsArray.forEach(name => console.log(name))
// "Jon"
// "Doyt"
// "cherry"

7.indexOf()

The indexOf() function accepts a parameter and the index of the item or -1 if it does not exist.

const bestFriends = ['ant', 'bison', 'camel', 'duck', 'bison'];
console.log(bestFriends.indexOf("bison"))

8.join()

The join method concats all array elements into a single string with a separator.

const arrays3 = ['Fire', 'Air', 'Water'];
console.log(arrays3.join())
// "Fire,Air,Water"

9.map()

The map() function it’s loop throw all array element and return a new array based on a transformation with each item.

let numsArray = [1, 2, 3, 4];
const singleValue = numsArray.map((num) => num + 1);
console.log(singleValue);//[ 2, 3, 4, 5 ]

10.lastIndexOf()

The lastIndexOf() method works like the indexOf method but the main difference between indexOf the method search form beginning to end, and lastIndexOf() method searches end to beginning.

const movies = ["Avangers", "Thor","Ant Man", "Thor"];
console.log(movies.lastIndexOf("Thor"));//3

11.pop()

The pop() method removes the last elements from the array.

const movies = ["Avangers", "Thor", "AntMan", "SpiderMan"];
// ["Avangers", "Thor", "AntMan", "SpiderMan"];movies.pop();
//[ 'Avangers', 'Thor', 'AntMan' ]

12.push()

The push method adds an element to the end of the array position and returns a new array.

const movies = ["Avengers", "AntMan", "SpiderMan"];
// ["Avengers", "AntMan", "SpiderMan"];movies.push("Thor");
// ["Avengers", "AntMan", "SpiderMan", "Thor"];

13.reduce()

The method does a function on every element of the array, occurring in a single amount value.

const number = [1, 2, 3, 4];
const sum = number.reduce((accumulator, currentValue) => {
  return accumulator + currentValue;
});
console.log(sum); //10

14.reverse()

The reverse method reverses the index of the element in the array.

const number = [1, 2, 3, 4];
const reversed = number.reverse();
console.log(reversed); //[ 4, 3, 2, 1 ]

15.shift()

The shift method removes the first element in an array.

const friends = ["Nahid", "Sagor", "Jahid"];
friends.shift();
console.log(friends); //[ 'Sagor', 'Jahid' ]

16.slice()

The slice method accepts two parameters starting and ending positions. it returns a new array without the starting and ending position elements.

const candidate = ["Sagor", "Jahid", "JonDoe"];
const selectedCandidate = candidate.slice(0, 2);
console.log(selectedCandidate); //[ 'Sagor', 'Jahid' ]

17.sort()

The sort() method sorts elements in an array with order base. But we can pass a callback function to define which patters sorted our data.

let numbers = [4, 2, 5, 1, 3];
numbers.sort((a, b) => a - b);
console.log(numbers); //[ 1, 2, 3, 4, 5 ]

18.splice()

The splice method accepts a minimum of 2 parameters index and how many elements remove from an array. This function mutates the array.

const months = ["Jan", "March", "April", "June"];
months.splice(3, 0, "Feb");
console.log(months); //[ 'Jan', 'March', 'April', 'Feb', 'June' ]

19.unshift()

The unshift method adds elements in the beginning position of an array and returns a new array length.

let numbers = [2, 3, 4];
numbers.unshift(1);
console.log(numbers); //[ 1, 2, 3, 4 ]

JavaScript Object methods

1.Object.assign()

Create a new object from multiple objects.

const person = { name: "Jobayer Hossain", id: 23 };
const address = { city: "Dhaka", age: 35 };
const info = Object.assign(person, address);
console.log(info);
//{ name: 'Jobayer Hossain', id: 23, city: 'Dhaka', age: 35 }

2.Object.freeze()

The Object.freeze method freezes all object all properties.

const person = {
 name: "Jon Doe",
 designation: "Front-End Developer",
 skill: { 
   design: "Photoshop",
   codeing: "Javascript",
  },};

Object.freeze(person);
person.name = "Jobayer Hossain";
person.skill.design = "Figma";

console.log(person);
/*{
  name: 'Jon Doe',
  designation: 'Front-End Developer',
  skill: { design: 'Figma', codeing: 'Javascript' }
}*/

3.Object.keys()

Object.keys() returns all the keys of an object.

const person = {
  name: "Jobayer Hossain",
  age: 21,
  role: "Front-End Developer",
  skill: "HTML CSS JS React",
};
const ObjKeys = Object.keys(person);
console.log(ObjKeys); //[ 'name', 'age', 'role', 'skill' ]

4.Object.values()

Object.values() returns all the values of an object.

const person = {
 name: "Jobayer Hossain",
 age: 21,
 role: "Front-End Developer",
 skill: "HTML CSS JS React",
};
const ObjValue = Object.values(person);
console.log(ObjValue);
//['Jobayer Hossain',21,'Front-End Developer','HTML CSS JS React']

JavaScript Math

1.Math.abs()

Math.abs() method returns the absolute value of a number .

console.log(Math.abs(5 - 2)); //3
console.log(Math.abs(5.9 - 5.1)); //0.8000000000000007

2.Math.sin()

This method returns a numeric value within -1 and 1, which describes the sine in radians.

console.log(Math.sin(1)); //0.8414709848078965
console.log(Math.sin(-1)); //-0.8414709848078965
console.log(Math.sin(0)); //0

2.Math.cos()

The cos() method returns the cosine of a number.

const getRadius = (a, b) => {return Math.cos(a) * b;};
console.log(getRadius(1, 10)); //5.403023058681398

3. Math.exp()

The exp() method returns e^[number].

console.log(Math.exp(5)); //148.4131591025766
console.log(Math.exp(6)); //148.4131591025766

4.Math.floor()

floor() method rounds a number down.

console.log(Math.floor(5.0524352345)); //5

5.Math.log()

The log() method returns the common logarithm of a number.

console.log(Math.log(4)); //1.3862943611198906

6.Math.min()

The Math.min() method accepts a value as a parameter and it returns the lowest value.

console.log(Math.min(5, 10)); //5
console.log(Math.min(87, 210)); //87

7.Math.max()

The Math.max() method accepts a value as a parameter and it returns the highest value.

console.log(Math.max(5, 10)); //10
console.log(Math.max(87, 210)); //210

8.Math.random()

Respond to a random number between 0 and 1.

console.log(Math.random()); //0.9671211951447136
console.log(Math.random()); //0.8787034350662186
console.log(Math.random()); //0.2373625260886849

9.Math.round()

The round() method rounds a number.

console.log(Math.round(2.9)); // 3
console.log(Math.round(2.5)); // 3
console.log(Math.round(2.4)); // 2

10.Math.sqrt()

The sqrt() method returns the square root of a number:

console.log(Math.sqrt(16)); //4
console.log(Math.sqrt(81)); //9