Javascript calculator...can't implement switching operators

[Siegeprogrammer]

@vipatron

import React from "react";
import ReactDOM from "react-dom";

import "./styles.css";

// a decimal after a decimal between two digit strings
// two decimals in a row
// two of the SAME operator in a row(summing up four repetitive regexes)
// multiply or divide if no digit has been entered since power on / clear
// two zeroes at the beginning of the string(doesn’t cover the case of “5 + 005”)
// two zeroes at the beginning of a generic digit string(using positive lookbehind when lookbehind isn’t supported on all javascript engines)

var regex = /(\d*\.\d+\.)|\.{2,}|\+{2,}|-{2,}|\*{2,}|^[*/]|^00|(?<=[/+\-*])0{2}/g;
// var regex = /a/g;
// tests for an operator
var operatorRegex = /[*\/\-\+]/;
// tests whether a operator is the last character in inputString
var operatorLast = /[*\/\-\+]$/;

class Calculator extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      inputString: ""
    };
    this.handleInput = this.handleInput.bind(this);
    this.handleClear = this.handleClear.bind(this);
    this.handleEquals = this.handleEquals.bind(this);
  }

  handleInput(event) {
    // console.log(this.state.inputString)
    // if (!regex.test(this.state.inputString)) { //If our 'patterns we don't want ' regex doesn't match anything
      if (
        operatorRegex.test(event.target.value) && //If event value passed in is an operator
        operatorLast.test(this.state.inputString) //If the last value of our inputString is an operator
      ) {
        this.setState({
          inputString: this.state.inputString.replace(
            //replace the old operator with thte new one that was clicked
            operatorLast,
            event.target.value
          )
        });
      } else {
        this.setState({
          inputString: this.state.inputString + event.target.value
        });
      }
    // }
  }

/* 
handleClear will change inputString to it's defined state of "" which is what the tests call for
Displying 0 in the view is taken care of via the ternary operTION in the display declaration
*/

  handleClear(event) {
    this.setState({
      inputString: ""
    });
  }

  handleEquals() {
    this.setState({
      inputString: eval(this.state.inputString)
    });
  }



  // shouldComponentUpdate() {
  //   let regex = /(\d*\.\d*\.)|\.{2}|\+{2}|\-{2}|^[*\/]|^00|(?<=\b)0{2}/g;
  //   return !regex.test(this.state.inputString);
  // }

  render() {
    return (
      <div className="Calc">
        <button id="equals" value="=" onClick={this.handleEquals}>
          =
        </button>
        <button id="zero" onClick={this.handleInput} value="0">
          0
        </button>
        <button id="one" onClick={this.handleInput} value="1">
          1
        </button>
        <button id="two" onClick={this.handleInput} value="2">
          2
        </button>
        <button id="three" onClick={this.handleInput} value="3">
          3
        </button>
        <button id="four" onClick={this.handleInput} value="4">
          4
        </button>
        <button id="five" onClick={this.handleInput} value="5">
          5
        </button>
        <button id="six" onClick={this.handleInput} value="6">
          6
        </button>
        <button id="seven" onClick={this.handleInput} value="7">
          7
        </button>
        <button id="eight" onClick={this.handleInput} value="8">
          8
        </button>
        <button id="nine" onClick={this.handleInput} value="9">
          9
        </button>
        <button id="add" value="+" onClick={this.handleInput}>
          +
        </button>
        <button id="subtract" value="-" onClick={this.handleInput}>
          -
        </button>
        <button id="divide" value="/" onClick={this.handleInput}>
          /
        </button>
        <button id="multiply" value="*" onClick={this.handleInput}>
          *
        </button>
        <button id="decimal" value="." onClick={this.handleInput}>
          .
        </button>
        <button id="clear" onClick={this.handleClear}>
          AC
        </button>
        <div id="display">
          {this.state.inputString === "" ? 0 : this.state.inputString}
        </div>
      </div>
    );
  }
}

const rootElement = document.getElementById("root");
ReactDOM.render(<Calculator />, rootElement);

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