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Object.seal() in JavaScript

Did you know Object.seal() in JavaScript

My new favorite JavaScript feature is the Object.seal() method. I’ve used the Object.freeze() sometimes but, this is something new and I feel it can be really handy in many cases where we have a pre-defined object template to use and only want to change the values of its existing properties.

Sealing an Object with the seal() method

As the name says, we can seal a javascript object using the Object.seal() method. This means that once an object is sealed
1. We cannot add new properties to the object
2. Existing properties cannot be modified
3. But, the value of existing properties can be changed

How to seal an Object in JavaScript

const siteObject = {
   name: "matrixread",
   posts:100
};

Object.seal(siteObject);
// Object is sealed now

siteObject.posts = 200; 
// We can modify existing properties

siteObject.author = "Abhiram Reddy"
// We cannot add a new property
delete  siteObject.name;
// We cannot delete existing proprties

console.log(siteObject);
// Output 
// { name: 'matrixread', posts: 200 }

Object.seal() vs Object.freeze()

Object.freeze() is almost the same as Object.seal() but when an object is frozen we cannot modify even the values of the properties. This means that once an object is frozen.

  1. We cannot add new properties to the object
  2. Existing properties cannot be modified
  3. The values of existing properties cannot be changed
const siteObject = {
    name: "matrixread",
    posts:100
 };

 Object.freeze(siteObject);
 // Object is Frozen now

 siteObject.posts = 200; 
 // We cannot modify existing properties

 siteObject.author = "Abhiram Reddy"
 // We cannot add a new property

 delete  siteObject.name;
 // We cannot delete existing proprties

 console.log(siteObject);
 // Output 
 // { name: 'matrixread', posts: 100 }

As we can learn from the output that the Object remained the same, not even the existing property values can be changed once an object is frozen.

Reference

Object.seal() at MDN

Conclusion

I can’t wait to use the Object.seal() method in my code as it makes the whole object structure fixed and even prevents us from making changes by accident. What do you think?

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