reactjs - Calc App React Undefined -

i creating calculator in react , have state value of displayvalue , keeps returning undefined when perform 1 of operationsmethod. unsure doing incorrectly if can appreciated thanks.

i thinking has performoperation method unsure what.

export default class app extends component {   constructor(props) {     super(props)      this.state = {displayvalue: '0' , waitingforoperand: false, operator: null, value: null}     this.inputdigit = this.inputdigit.bind(this);     this.inputdot = this.inputdot.bind(this);     this.clear = this.clear.bind(this);     this.togglesign = this.togglesign.bind(this);     this.performoperation =  this.performoperation.bind(this);   }    clear() {     const {displayvalue} =  this.state;     this.setstate({       displayvalue: '0'     });   }    inputdigit(digit) {     const {displayvalue, waitingforoperand} = this.state;     if(waitingforoperand) {       this.setstate({         displayvalue: string(digit),         waitingforoperand: false       });     } else {     this.setstate({       displayvalue: displayvalue === '0' ? string(digit) : displayvalue + digit     });   }   }    inputdot() {     const {displayvalue, waitingforoperand} =  this.state;     if(waitingforoperand) {       this.setstate({         displayvalue: '.',         waitingforoperand: false       });     }     else if(displayvalue.indexof('.') === -1) {       this.setstate({         displayvalue: displayvalue + '.'       });     }   }    togglesign() {     const {displayvalue} = this.state;      this.setstate({       displayvalue : displayvalue.charat(0) === '-' ? displayvalue.substring(1) : '-' + displayvalue      })   }    percent() {     const {displayvalue} = this.state;     const value = parsefloat(displayvalue);      this.setstate({       displayvalue: string(value / 100)     });   }    performoperation(nextoperator) {     const {displayvalue, operator, value} = this.state;     const nextvalue = parsefloat(displayvalue);      const operations = {       '/' : (prevval, nextvalue) => prevval / nextvalue,       '*' : (prevval, nextvalue) => prevval * nextvalue,       '+' : (prevval, nextvalue) => prevval + nextvalue,       '-' : (prevval, nextvalue) => prevval - nextvalue,       '=' : (prevval, nextvalue) => nextvalue     }      if(value == null) {       this.setstate({         value: nextvalue       });      } else if(operator) {       const currentvalue = value || 0;       const computedvalue = operations[operator](currentvalue, computedvalue);        this.setstate({         value: computedvalue,         displayvalue: string(computedvalue)       })      }      this.setstate({         waitingforoperand: true,       operator: nextoperator     })   } 

there problem line in performoperations

const computedvalue = operations[operator](currentvalue, computedvalue); 

it should be:

const computedvalue = operations[operator](nextvalue, currentvalue); 

anyway, variable names bit misleading.