score:0

first, you have an error in
<input type="submit" value="check" onclick={this._showmessage{this._checkvalue} />
next,
<input> boxes in react works a little bit differently. check out this link

score:2

you have a typo in your code:

_checkvalue() {
  if (evt.taget.value != number) {
  // -------^ should be target

also, number.isnan would be a more robust comparison.


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