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Understanding setInterval in React component [duplicate]

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I am learning React and in general Javascript so my apologies if it is very obvious.

I have a React Clock Component that is suppose to update the timer.

componentDidMount()
this.timer = setInterval(this.tick, 1000);


componentWillUnmount()
clearInterval(this.timer);


tick()
this.setState(
date: new Date()
);



This throws the error that setState is not a function.

setState

However if i change the code of setInterval like this

componentDidMount()
this.timer = setInterval(() => this.tick(), 1000);



It works fine.

I am confused, as per my understanding setInterval needs a function and timer. Why if i provide the function name this.tick it doesn't work. Why I have to wrap it in another anonymous function. I am from PHP background and in PHP we can pass other function names where it needs a callback parameter.

setInterval

this.tick

Thanks

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