[Javascript][Lecture][드림코딩]자바스크립트 기초 강의(ES5+)(9/13)

9. 유용한 10가지 배열 함수들. Array APIs 총정리 | 프론트엔드 개발자 입문편 ( JavaScript ES6)

// Q1. make a string out of an array
{
  const fruits = ["apple", "banana", "orange"];
  // di it yourself!
  // console.log(fruits.toString()); // .join과 .toString의 차이는 구분자(seperator)
  // answer
  const result = fruits.join(" and ");
  console.log(result);
}

// Q2. make an array out of a string
{
  const fruits = "🍎, 🥝, 🍌, 🍒";
  // do it yourself!
  // const fruit = fruits.split(",");
  // console.log(fruit);
  // answer
  const fruit = fruits.split(",");
  console.log(fruit);
}

// Q3. make this array look like this: [5, 4, 3, 2, 1]
{
  const array = [1, 2, 3, 4, 5];
  // do it yourself!
  // const reverseArray = array.reverse();
  // console.log(reverseArray);
  // answer
  const reverseArray = array.reverse();
  console.log(reverseArray);
  console.log(array); // 원래 배열도 바뀐다.
}

// Q4. make new array without the first two elements
{
  const array = [1, 2, 3, 4, 5];
  // do it yourself!
  // const result = array.slice(2);
  // const resultNew = array.slice(2, 5);
  // console.log(result);
  // console.log(resultNew);
  // // answer
  const result = array.slice(2, 5);
  console.log(result);
  console.log(array);
}

// -------------------------------------------------------------
class Student {
  constructor(name, age, enrolled, score) {
    this.name = name;
    this.age = age;
    this.enrolled = enrolled;
    this.score = score;
  }
}
const students = [
  new Student("A", 29, true, 45),
  new Student("B", 28, false, 80),
  new Student("C", 30, true, 90),
  new Student("D", 40, false, 66),
  new Student("E", 18, true, 88),
];

// Q5. find a student with the score 90
{
  // do it yourself!
  // for (let i = 0; i < students.length; i++) {
  //   if (students[i].score === 90) {
  //     console.log(students[i]);
  //   }
  // }
  // answer
  // const result = students.find(function (value) {
  //   return value.score === 90;
  // });
  const result = students.find((value) => value.score === 90);
  console.log(result);
}

// Q6. make an array of enrolled students
{
  // do it yourself!
  // const result = students.filter((value) => value.enrolled === true);
  // console.log(result);
  // // answer
  const result = students.filter((student) => student.enrolled === true);
  console.log(result);
}

// Q7. make an array containing only the students' scores
// result should be: [45, 80, 90, 66, 88]
{
  // do it yourself!
  // let result = [];
  // for (let i = 0; i < students.length; i++) {
  //   result.push(students[i].score);
  // }
  // console.log(result);
  // answer
  const result = students.map((student) => student.score);
  console.log(result);
}

// Q8. check if there is a student with the score lower than 50
{
  // do it yourself!
  // const result = students.some((student) => student.score < 50);
  // console.log(result);
  // answer
  const result = students.some((student) => student.score < 50);
  console.log(result);

  const result2 = !students.every((student) => student.score >= 50);
  console.log(result2);
}

// Q9. compute students' average score
{
  //do it yourself!
  // let result = 0;
  // for (let i = 0; i < students.length; i++) {
  //   result += students[i].score;
  // }
  // console.log(result / 5);
  // answer
  // const result = students.reduce((prev, curr) => {
  //   console.log("----------");
  //   console.log(prev);
  //   console.log(curr);
  //   return prev + curr.score;
  // }, 0);
  const result = students.reduce((prev, curr) => prev + curr.score, 0);
  console.log(result / students.length);
}

// Q10. make a string containing all the scores
// result should be: '45, 80, 90, 66, 88'
{
  // do it yourself!
  // const result = students.map((student) => student.score);
  // const resultArray = result.join();
  // console.log(resultArray);
  // answer
  const result = students
    .map((student) => student.score)
    // .filter((score) => score >= 50)
    .join();
  console.log(result);
}

// Bonus! do Q10 sorted in ascending order
// result should be: '45, 66, 80, 88, 90'
{
  // do it yourself!
  // const result = students
  //   .map((student) => student.score)
  //   .sort((a, b) => a - b)
  //   .join();
  // console.log(result);
  // answer
  const result = students
    .map((student) => student.score)
    .sort((a, b) => a - b)
    .join();
  console.log(result);
}