함수(Functions)_2

1. 명령형 프로그래밍보다 함수형 프로그래밍.

//Bad👎
const programmerOutput = [
  {
    name: 'Uncle Bobby',
    linesOfCode: 500
  }, {
    name: 'Suzie Q',
    linesOfCode: 1500
  }, {
    name: 'Jimmy Gosling',
    linesOfCode: 150
  }, {
    name: 'Gracie Hopper',
    linesOfCode: 1000
  }
];

let totalOutput = 0;

for (let i = 0; i < programmerOutput.length; i++) {
  totalOutput += programmerOutput[i].linesOfCode;
}


//Good👍
const programmerOutput = [
  {
    name: 'Uncle Bobby',
    linesOfCode: 500
  }, {
    name: 'Suzie Q',
    linesOfCode: 1500
  }, {
    name: 'Jimmy Gosling',
    linesOfCode: 150
  }, {
    name: 'Gracie Hopper',
    linesOfCode: 1000
  }
];

const totalOutput = programmerOutput
  .map(programmer => programmer.linesOfCode)
  .reduce((acc, linesOfCode) => acc + linesOfCode, INITIAL_VALUE);

12. 조건문을 캡슐화.

//Bad👎
if (fsm.state === 'fetching' && isEmpty(listNode)) {
  // ...
}


//Good👍
function shouldShowSpinner(fsm, listNode) {
  return fsm.state === 'fetching' && isEmpty(listNode);
}

if (shouldShowSpinner(fsmInstance, listNodeInstance)) {
  // ...
}

13. 부정조건문 피하기.

//Bad👎
function isDOMNodeNotPresent(node) {
  // ...
}

if (!isDOMNodeNotPresent(node)) {
  // ...
}

//Good👍
function isDOMNodePresent(node) {
  // ...
}

if (isDOMNodePresent(node)) {
  // ...
}

14. 조건문 작성 피하기.

//Bad👎
class Airplane {
  // ...
  getCruisingAltitude() {
    switch (this.type) {
      case '777':
        return this.getMaxAltitude() - this.getPassengerCount();
      case 'Air Force One':
        return this.getMaxAltitude();
      case 'Cessna':
        return this.getMaxAltitude() - this.getFuelExpenditure();
    }
  }
}

//Good👍
class Airplane {
  // ...
}

class Boeing777 extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getPassengerCount();
  }
}

class AirForceOne extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude();
  }
}

class Cessna extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getFuelExpenditure();
  }
}

15. 타입-체킹을 피하라.

• 일관성 있는 API 사용.

//Bad👎
function travelToTexas(vehicle) {
  if (vehicle instanceof Bicycle) {
    vehicle.pedal(this.currentLocation, new Location('texas'));
  } else if (vehicle instanceof Car) {
    vehicle.drive(this.currentLocation, new Location('texas'));
  }
}

  
//Good👍
function travelToTexas(vehicle) {
  vehicle.move(this.currentLocation, new Location('texas'));
}

• TypeScript 도입 고려.

//Bad👎
function combine(val1, val2) {
  if (typeof val1 === 'number' && typeof val2 === 'number' ||
      typeof val1 === 'string' && typeof val2 === 'string') {
    return val1 + val2;
  }
  
  throw new Error('Must be of type String or Number');
}

  
//Good👍
function combine(val1, val2) {
  return val1 + val2;
}