I am reading the Facebook tutorial for React. About 40% of the way through, there's a section called Why Immutability is Important where they state (regarding the importance of immutability):

The end result is the same but by not mutating (or changing the underlying data) directly we now have an added benefit that can help us increase ponent and overall application performance.

My question is: why/how? That is, in React, specifically why/how does immutability (using Object.assign(...), etc.) "help increase...overall application performance"?

I am reading the Facebook tutorial for React. About 40% of the way through, there's a section called Why Immutability is Important where they state (regarding the importance of immutability):

The end result is the same but by not mutating (or changing the underlying data) directly we now have an added benefit that can help us increase ponent and overall application performance.

My question is: why/how? That is, in React, specifically why/how does immutability (using Object.assign(...), etc.) "help increase...overall application performance"?

• javascript
• performance
• reactjs
• immutability

Share Improve this question Follow asked Jan 3, 2017 at 12:18 smeebsmeeb 29.7k7171 gold badges274274 silver badges474474 bronze badges 1

• The subsection titled Tracking Changes seems to explain it quite well IMO - is it unclear, or are you asking for a more technically detailed explanation? – UnholySheep Commented Jan 3, 2017 at 12:22

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I think that it is easier to understand with arrays:

Imagine that you have an array, containing many, many entries. You replace one entry with another - to see if anything changed react has to loop through the whole array.

Now, imagine that everytime you make some changes you create new array - then the only thing react has to do is to pare references

Object.assign does the same - instead of changing existing object, you create a new one, so that react can detect changes simply by paring references