Some Important Javascript Method

Some important JavaScript are -

1) String.slice():

It copies a section of a string and return it as a new string without modifying the original string.

Syntax:

string.slice(start,end)

Example:

const str = “Hello Bangladesh”;

console.log(str.slice(0,6));

//output:Hello

2) Global isNaN() Vs Number.isNaN():

isNaN is function that checks whether given value is a valid number or not. If the value is invalid number (Not-a-number) then it returns true otherwise it returns false.

Here, the global function isNaN(), first converts the tested value to a number and then evaluate it but Number.isNaN() directly tests it without any conversion.

Example:

console.log(isNaN(new Date().toString()));

//string converted to number and return true

console.log(Number.isNaN(new Date().toString()));

//return false

3) Array.splice():

This method changes the existing array by removing or replacing the array.

Syntax:

Array.splice( index, remove_count, item_list )

Example:

let languages = [‘C++’, ‘Java’, ‘Html’, ‘Python’, ‘C’];

// Add ‘javascript’ and ‘Php’ after removing ‘Html’.

let removed = languages.splice(2, 1, ‘javascript’, ‘Php’)

4) Array.join():

This method creates a string by concatenating the array element using an optional separator parameter.

Example:

const arr = [“amar”,”sonar”,”bangla”];

console.log(arr.join(“-”));

//output: amar-sonar-bangla

5) Array.shift() and unshift():

Shift() method deletes the first element of an array. Unshift() method add a new element at first index of an array.

Example:

const arr = [“amar”,”sonar”,”bangla”];

const del = arr.shift();

console.log(arr);

//output:[ ‘sonar’, ‘bangla’ ]

const add = arr.unshift(“bangladesh”);

console.log(arr);

//output: [ ‘bangladesh’, ‘sonar’, ‘bangla’ ]

6) Object.assign():

This method is used to copy one or more source objects to a target object. It takes source objects and a target object as parameters and push the source objects into the target object and display the target object.

Example:

const target = { a: 1, b: 2 };

const source = { b: 4, c: 5 };

const returnedTarget = Object.assign(target, source);

console.log(target);

//output: { a: 1, b: 4, c: 5 }

console.log(returnedTarget);

//output: { a: 1, b: 4, c: 5 }

Here is a warning for deep cloning, If the source value is a reference to an object, it only copies the reference value.

Example:

let obj1 = { a: 0 , b: { c: 0}};

let obj2 = Object.assign({}, obj1);

console.log(JSON.stringify(obj2)); // { “a”: 0, “b”: { “c”: 0}}

obj2.b.c = 3;

console.log(JSON.stringify(obj1)); // { “a”: 1, “b”: { “c”: 3}}

console.log(JSON.stringify(obj2)); // { “a”: 2, “b”: { “c”: 3}}

7) Object.create():

This method creates a new object, with the specified prototype. Newly created object can access all the properties of prototype object. It can take an optional parameter to add new properties.

Example:

const fruits = {test:’sour’}

const mango = Object.create(fruits, {

name:{value:’Rajshahi mango’}

});

console.log(‘name: ‘+mango.name + ‘, test: ‘+ mango.type)

//output: name: Rajshahi mango, test: sour

8) Object.values() and Object.keys():

These methods return an array with values and keys of the object.

Example:

const object1 = {

a: ‘somestring’,

b: 42,

c: false

};

console.log(Object.values(object1)); // output:[“somestring”, 42, false]

console.log(Object.keys(object1)); //output: [“a”, “b”, “c”]

9) Object.freeze()

This method freezes an object. A frozen object can no longer be changed;

Example:

const obj = { prop: 42 };

Object.freeze(obj);

obj.prop = 33;

// Throws an error in strict mode

console.log(obj.prop);

// expected output: 42

10) Math.round():

It returns the value of a number rounded to the nearest integer.

Example:

console.log(Math.round(0.9));

//output: 1

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