JavaScript Object is a non-primitive data type we store in it multiple and different primitive data type, every object consists of keys (properties) and its values, here is an object example👇

const person = {
  firstName: "Ismail",
  lastName: "AbuAlmagd",
  age: 35,
  married: true
};

Loop throw object JavaScript:

there are many ways to iterate over JavaScript object, let me show it👇

1-Usingfor...in: this statement allows us to iterate over all object properties 👇

for (let key in person) {
    console.log(key, person[key]);
}

/*output👇
firstName Ismail
lastName AbuAlmagd
age 35
married true
*/

2.UsingObject.entries(): this statement provided at (ES6), with this statement you can get key and value directly👇

 for (let [key, value] of Object.entries(person)) {
    console.log(key, value);
}

/*output
firstName Ismail
lastName AbuAlmagd
age 35
married true
*/

3.extracte keys into array by Object.keys then get value by index👇

let keys = Object.keys(person);

// Iterate over properties by index
for (let i = 0; i < keys.length ; i++) {
    console.log(keys[i], person[keys[i]]);
}

/*output
firstName Ismail
lastName AbuAlmagd
age 35
married true
*/

Check if key exists in object JavaScript:

there are many ways to check if key exists in object let me show you👇

1-Using hasOwnProperty() 👇

if (person.hasOwnProperty('firstName')) {
       console.log('person object has  a fristName key');
    }else{
      console.log('person object has  no key equal to fristName');
    }

/*output
person object has  a fristName key
*/




if (person.hasOwnProperty('secondName')) {
       console.log('person object has  a secondName key');
    }else{
      console.log('person object has  no key equal to secondName');
    }
/*output
person object has  no key equal to secondName
*/

2.Usinginoperator:

if ('firstName' in person) {
       console.log('person object has  a fristName key');
    }else{
      console.log('person object has  no key equal to fristName');
    }

/*output
person object has  a fristName key
*/




if ('secondName' in person) {
       console.log('person object has  a secondName key');
    }else{
      console.log('person object has  no key equal to secondName');
    }
/*output
person object has  no key equal to secondName
*/

Difference betweeninandhasOwnProperty()thatinwork even for inherited, On the contraryhasOwnProperty()didn't.

3-As you can get value of object key by using Square Brackets, so we can check if object have this key or not,

Checking undefined-ness is not accurate as may be the key exist but undefined👇

const cat={
fristName:"brodi",
age:1,
secondName:undefined
}

if(cat['secondName']===undefined){
console.log('the secondName key may didnot exist in person object or exist but hasnot a value ')
}

Delete key from object JavaScript:

1**-Using** deleteoperator:

const person={
fristName:"ali",
age:12,
secondName:"mina"
}

delete person['age'];

console.log(person);
/*output
{ fristName: 'ali', secondName: 'mina' }
*/

2-Using object destructing:

This way is immutable, mean we create a new object.

const person={
fristName:"ali",
age:12,
secondName:"mina"
}


const{age:_,...newPerson}=person;

console.log(newPerson);

/*output
{ fristName: 'ali', secondName: 'mina' }
*/

If we print the person, the old object it's still unmodified.

console.log(person);

/*output
{ fristName: 'ali', age: 12, secondName: 'mina' }
*/

I hope this is useful to you.

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thanks, stay in touch ismail abo almagd or @SaaSboy on Twitter.