JS 기초 강의(ES5+) - # Function expression (5)

1. 다양한 함수 표현 - Function expression

• a function declaration can be called earlier than it is defined. (hoisted)
• a function expression is created when the execution reaches it

  const print = function () {
    // anonymous function
    console.log('print');
  };
  print();
  const printAgain = print;
  printAgain();
  const sumAgain = sum;
  console.log(sumAgain(1, 3));

2. Callback function using function expression

• function randomQuiz(answer, printYes, printNo) {
    if (answer === 'love you') {
      printYes();
    } else {
      printNo();
    }
  }

• anonymous function

  const printYes = function () {
    console.log('yes!');
  };

• named function (better debugging in debugger's stack traces, recursions)

  const printNo = function print() {
    console.log('no!');
  };
  randomQuiz('wrong', printYes, printNo);
  randomQuiz('love you', printYes, printNo);

• Arrow function (always anonymous)

  // const simplePrint = function () {
  //   console.log('simplePrint!');
  // };
  
  const simplePrint = () => console.log('simplePrint!');
  const add = (a, b) => a + b;
  const simpleMultiply = (a, b) => {
    // do something more
    return a * b;
  };

• 함수 선언하고, 바로 실행하기 - IIFE: Immediately Invoked Function Expression

  (function hello() {
    console.log('IIFE');
  })();

3. 계산기 함수 만들기

• function calculate(command, a, b)

  function calculate(command, a, b) {
    switch (command) {
      case 'add':
        return a + b;
      case 'substract':
        return a - b;
      case 'divide':
        return a / b;
      case 'multiply':
        return a * b;
      case 'remainder':
        return a % b;
      default:
        throw Error('unknown command');
    }
  }
  console.log(calculate('add', 2, 3)); // -> [5]