[TIL] 011. JavaScript - Array methods 익히기

Array.filter

1

  var snacks = ['새우깡', '프링글스', '감자깡', '꿀꽈배기', '콘칩', '허니버터칩'];
	
  const result = snacks.filter(snack => snack.length > 3);
  console.log(result); // ['프링글스', '꿀꽈배기', '허니버터칩'] 출력

2

  function aboveEighteen(number) {
    return number > 18;
  }
  let numbers = [12, 5, 8, 33, 22, 18].filter(aboveEighteen);
  console.log(numbers); // [12, 5, 8, 22] 출력

3

  function isEven(number) {
    return number % 2 == 0; // 짝수
  }
  let filtered_numbers = [10, 1, 3, 0, -10, 22, 900].filter(isEven);
  console.log(numbers); // [10, 0, -10, 22, 900] 출력

4

  var snacks = ['새우깡', '매운 새우깡', '감자깡', '꿀꽈배기', '콘칩', '매운 감자깡'];

  const filterItems = (query) => {
    return snacks.filter(snack => snack.indexOf(query) > -1);
  }
  console.log(filterItems('매운')); // ['매운 새우깡', '매운 감자깡'] 출력

5

  var students = [
    {id: 1, name: 'james', age: 30},
    {id: 2, name: 'tim', age: 29},
    {id: 3, name: 'john', age: 40},
    {id: 4, name: 'brian', age: 25}
  ]
  
  // const result = students.filter(student => student.age > 30);
  const result = students.filter(student => {
    return student.age > 30;
  });

  console.log(result); // ['john'] 출력

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Array.forEach

1

  let numbers = [1, 2, 3, 4, 5, 6, 7];
  
  numbers.forEach(number => console.log(number));
  
  // number.forEach(function (number){console.log(number); }); })
  // number.forEach(number => {console.log(number)});

2

  let fruits = ['banana', 'apple', 'orange', 'grape'];
  let fruits2 = ['cherry'];

  fruits.forEach(item => fruits2.push(item));
  console.log(fruits2); 
  // ['cherry', 'banana', 'apple', 'orange', 'grape'] 출력

3

  let sum = 0;
  let numbers = [20, 11, 33, 10, 7, 77];
  
  numbers.forEach(addTotal);

  function addTotal (number) {
    sum += number;
  }
  console.log(sum); // 158 출력

4

  let numbers = [20, 11, 33, 10, 7, 77];
  
  numbers.forEach((number, index, array) => {
    array[index] = number *2;
  });

  console.log(numbers);
  // [40, 22, 66, 20, 14, 154, 4]

---

Array.map

1

  var numbers = [4, 9, 16, 25, 36];
  var result = numbers.map(Math.sqrt); // 제곱근
  console.log(result); // [2, 3, 4, 5, 6] 출력

2

  var numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];

  // case 1
  var newNumbers = numbers.map(number => number + 2);

  // case 2
  var newNumbers = numbers.map(function(number){
    return number + 2;
  });
  
  // case 3
  var newNumbers = numbers.map(multiplyTwo);
  function multiplyTwo (number) {
    return number + 2;
  }

3

  var students = [
    {id: 1, name: 'james'},
    {id: 2, name: 'tim'},
    {id: 3, name: 'john'},
    {id: 4, name: 'brian'}
  ];

  var names = students.map(student => student.name);
  console.log(names) // ['james', 'tim', 'john', 'brian'] 출력

4

  var numbers = [1, 2, 3, 4, 5, 6];
  var numbersReverse = numbers.map(number => number * 2).reverse();
  console.log(numbersReverse); // [12, 10, 8, 6, 4, 2] 출력

5

  var numbers = [[1,2,3], [4,5,6], [7,8,9]];
  var newNumbers = numbers.map(array => array.map(number => number * 2));
  console.log(newNumbers);
  // [[2,4,6], [8,10,12], [14,16,18]] 출력

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출처

https://youtu.be/ZjH2yrA64TI