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JavaScript React Basics (2018) Understanding State Update State Based on Previous State

Samuel Marques
Samuel Marques
1,023 Points
Posted by Samuel Marques
Samuel Marques
1,023 Points

How to make the decrement not exceed 0?

If the score has reached 0, how to do it if the user continues clicking on the "-", the score does not go to -1, -2, -3 etc.

I tried this, but not working:

  decrementScore() {
    this.setState( prevState => {
      if (prevState >= 0) {
        return {
          score: prevState.score - 1
        }
      }
    })
  }

Thanks!

Joshua Blasbalg
.a{fill-rule:evenodd;}techdegree seal-36
Joshua Blasbalg
Full Stack JavaScript Techdegree Graduate 22,583 Points

hey samuel! without seeing the rest of your code, i would try (prevState != 0), so that if prevState is 0, the function won't work so it will never go to negative!

3 Answers

Samuel Marques
Samuel Marques
1,023 Points
Samuel Marques
Samuel Marques
1,023 Points

I put together the two answers and it was like this:

  decrementScore() {
    this.setState( prevState => {
      if (prevState.score !== 0) {
        return {
          score: prevState.score - 1
        }
      }
    })
  }

Thanks Guys; Works fine now

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

Samuel Marques — Glad to help. You can mark a question solved by choosing a "best answer".

And happy coding!

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

If "prevState" is an object that contains a "score" property, you wouldn't want to compare it directly to a numeric value. You should compare its "score" property instead.

But you can simplify the process a bit by checking the value before you call "setState", and only call it if the current value is greater than 0.

Matthew Conrad
Matthew Conrad
28,069 Points
Matthew Conrad
Matthew Conrad
28,069 Points

I guess a ternary operator also works:

  decrementScore = () => {
    this.setState(prevState => ({
      score: (prevState.score > 0) ? prevState.score - 1 : prevState.score = 0
    }));
  }