Javascript Objects Cheatsheet

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With arrays, there are usually a set number of specific things you want to achieve. Below is a list of pretty much any action you would want to perform on objects, and how to do it in Javascript. If you have any more, please tell me via twitter and I will add them (along with a link to your social media of choice).

1. Update a Property of an Object

Use the = operator:


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    // Updates myAge to 2043
    object.myAge = 2043

2. Turn an Object's Keys into an Array

Use keys():


    let object = {
        'myName' : 'Name',
        'myAge' : 1043
    }

    // Returns [ 'myName', 'myAge' ];
    let keys = Object.keys(object);

3. Turn an Object's Values into an Array

Use values():


    let object = {
        'myName' : 'Name',
        'myAge' : 1043
    }

    // Returns [ 'Name', 1043 ];
    let values = Object.values(object);

4. Turn Array or Map sets into an Object

Use fromEntries:


    let arrSets = [ ['myName', 'Name'], ['myAge', 1043] ]

    /* Returns {
        'myName' : 'Name',
        'myAge' : 1043
    } */
    let generateObject = Object.fromEntries(arrSets);

5. Shallow Clone an Object

Use assign() or ...:


    let object = {
        'myName' : 'Name',
        'myAge' : 1043
    }

    // Creates a copy of object, which we can edit separately
    let newObject = Object.assign({}, object);

    // Creates a copy of object, which we can edit separately
    let anotherClone =  { ...object };

6. Deep Clone an Object with only variables

Use JSON.parse(JSON.stringify()):


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    // Creates a copy of object, which we can edit separately
    let newObject = JSON.parse(JSON.stringify(object));
    newObject.myName.FirstName = 'Hello';
    console.log(newObject, object);
    /*
    Returns {
      myAge: 1043,
      myName: {
        FirstName: "Hello",
        SecondName: "Surname"
      }
    }, {
      myAge: 1043,
      myName: {
        FirstName: "Name",
        SecondName: "Surname"
      }
    } */

7. Merge two objects into the original variable

Use assign():


    let object = { 'myName' : 'Name' }
    let objectTwo = { 'myAge' : 1043 }
    Object.assign(object, objectTwo);

    console.log(object, objectTwo);
    /* Returns {
        myAge: 1043,
        myName: "Name"
    }, {
        myAge: 1043
    } */

8. Merge two objects into a new variable

Use ....


    let object = { 'myName' : 'Name' }
    let objectTwo = { 'myAge' : 1043 }
    
    let newObject = { ...object, ...objectTwo }

    console.log(object, newObject);
    /* Returns {
        myName: "Name"
    }, {
        myName: "Name",
        myAge: 1043
    } */

Note: if you merge two objects with ..., and there are duplicate keys (i.e. both have myAge), the second Object will overwrite the first.

9. Prevent new items being added to an object, but allow previous items to be changed

Use preventExtensions():


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    Object.preventExtensions(object);

    // Throws a TypeError
    object.myLocation = '123 Fake Street';

10. Prevent any changes to an object

Use freeze():


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    Object.freeze(object);

    // Throws a TypeError
    object.myLocation = '123 Fake Street';
    // Throws a TypeError
    object.myAge = 2043

11. Turn Object into a String

Use JSON.stringify():


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    // Returns {"myName":{"FirstName":"Name","SecondName":"Surname"},"myAge":1043}
    console.log(JSON.stringify(object))

12. Turn String into an Object

Use JSON.parse():


    let stringObject = '{"myName":{"FirstName":"Name","SecondName":"Surname"},"myAge":1043}';

    /* Returns {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    } */
    console.log(JSON.parse(object))

13. Check if Object has a property

Use hasOwnProperty():


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    // Returns true
    console.log(object.hasOwnProperty('myName'))

14. Make a Property of an Object Unwritable so you can't change it

Use defineProperty() and change writable:


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    Object.defineProperty(object, 'myAge', {
        writable: false,
    });

    // object.myAge remains 1043
    object.myAge = 2043;

15. Ignore certain properties when using a for loop

Use defineProperty() and change enumerable. If we set enumerable to false, that item will be ignored in forEach loops.


    let object = {
        'myName' : {
            'FirstName' : 'Name',
            'SecondName' : 'Surname'
        },
        'myAge' : 1043
    }

    Object.defineProperty(object, 'myAge', {
        enumerable: false,
    });

    // Returns only 'myAge'
    Object.keys(object).forEach(function(item) {
        console.log(item);
    });

16. Convert Object to Array sets

Use entries():


    let object = {
        'myName' : 'Name',
        'myAge' : 1043
    }

    // Returns [ [ 'myName', 'Name' ], [ 'myAge', 1043 ]];
    let entries = Object.entries(object);

Last Updated 1613241721764