ReactJS and immutability -

i've learning reactjs while now. 1 of thing puzzles me why reactjs uses immutability in many aspects props, elements etc. there specific reason this? philosophy behind this?

when try add new property props i'm getting below error.

uncaught typeerror: can't add property me, object not extensible

react uses immutability obvious performance reasons. example

idea whenever setting state , dont mutate state clone part of , update state

for example

this.state = { entries: [1,2,3] } 

you should do

this.state.setstate({ entries: this.state.entries.slice().push(9); //not this.state.entries.push(9) }) 

performance gains achieved when use shouldcomponentupdate

in shouldcomponentupdate can compare references , not due deep checking

shouldcomponentupdate(prevstate,newstate){   return prevstate.entries != newstate.entries  }