D3: 조건문, 반복문, 함수

SUMMARY

• typeof: returns a string
  typeof 42, typeof 'hello', typeof true, typeof undeclaredVariable
• template literal can..
  • include functions/operations
  • print out function declarations/expressions!
• you declare a function with...
  • keyword ("function"), function name, parameters, code block to execute, return value
• function expressions: different way of declaring/expressing a function
• careful with while loops that do not specify an end point at which the loop should end (infinite loops)

• >= || <= (o) ; => (x)
• 동치연산자 (===, ==, !==, !=), 할당연산자 (=)
• you can include an operation (e.g. a * b) inside a template literal!
  • console.log(`${num} x ${i} = ${num * i}`);

---

삼항연산자

• a ? b : c

•   let num = 5;
    num % 2 === 0 ? console.log('짝수') : console.log('홀수'); // '홀수입니다.'

for-loop vs. while-loop

• while loop: when you're not sure how many times to repeat
• for loop:
  • when you're relatively sure of what you want to repeat
  • when you are going through a string or array
  • when you need nested for-loops
• know how to transform one into the other

for loop

• for (초기값; 조건식; 증감식) { // 실행할 코드 }
• index: str[num]; str.indexOf('a')
• you can nest as many for loops within a for loop!

while loop

• careful of infinite loops - check if the condition becomes false at a certain point
• do...while -> do is done at least once before evaluating the while condition

functions

• keyword (function) / name / parameter(s) (매개변수)
• you call/invoke (호출) a function with arguments (전달인자 - assigned values to parameters when calling a function), which returns a result
• 함수선언문 (function declaration) vs. 함수표현식 (function expression)
  - you can print a function (not the return value, but actual function declaration/expression) inside a template literal!
• scope: parameter names only work within the scope of the function
• you can assign the returned value of a called function into a variable