[Javascript ] 자바스크립트 배열 맛보기, All About Javascript Arrays

JavaScript 

• JavaScript는 웨페이지에서 복잡한 기능을 구현할 수 있도록 하는 객제현 스크린팅 프로그램밍 언어입니다.
• 자바스크립트는 동적이며, 타입을 명시할 필요가 없는 인터프리터 언어입니다.
• 자바스크립트는 객체 지향형 프로그래밍과 함수형 프로그래밍을 모두 표현할 수 있습니다.
• Interpreted Language as JavaScript, Python Ruby
• Compiled Languages: Java, C/C++, Swift 

 

 

 

Arrays

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• Arrays : a net way of strong a list items under a single variable name.
• Arrays are generally described as "list-like objects"
• Basically single objects that contain multiple values stored in a list.
• Can mix several data types string, number, objects

const array = [1, "Hello", [0,1,2]]

 

• Finding the length of a array : using array.length property.
• Start with 0, list number called index.
• Here interesting fact computers start count with 0;

 

• Array inside array called : Multidimensional Array 
• Special Point of Multidimensional arrays two sets of brackets []

const array[1, "Hello", [0,1,2]]
array[0] = 1 and array[1] is "Hello".

array[2][0] equal fist value of fist index as 0
array[2][1] is returns 1 and array[2][2] is returns 2

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• Finding the index of items in an array 
• index.of() method takes an item argument or returns "-1" when value not included

const fruit = ["banana", "apple", "orange", "kiwi"];

console.log(fruit.indexOf('banana')) => returns 1
console.log(fruit.indexOf('mango')) => returns -1, Not included

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•  Adding Items in an array
• Add one or more items to the end of an array we use push();

const num = [1,2,3]; // length = 3

num.push(5) // [1,2,3,5], length = 4

 

• Adding Items in start of array using unshift();

const num = [1,2,3];

num.unshift(5); // [5,1,2,3]

 

•  Removing items last item use pop();

const num = [1,2,3,5,70];

num.pop(); // [1,2,3,5];

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• The pop() method returns the deleted item.

const num = [1,2,3,5,70];
var deletedItem = num.pop();

console.log(deletedItem);  // 70

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• To Remove the first item of array use shift();

const num = [1,2,3,4];

num.shift(); // [2,3,4];

 

•  To Remove nth item in array using splice();
•  In this call splice(a,b) => a is as fist argument where to start removing and b shows how many items will delete 
•  if  (index != -1) =>  index == -1 means that not included, so index != -1 must include
       

const num = [1,2,3,4,70,100];

   const index = num.indexOf(3);
         if(index != -1){
            num.splice(index,2)
            
            // as splice() method here "index" is 2th as 3 
            // and "2" means will delete 2 items start 2th index that 3
            
         }

console.log(num); // [1,2,70,100], length is 4

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• Accessing every item , using for .. of method

const num = [1,2,70,100];

      for(const getIndex of num){
         console.log(getIndex);
         
         // result get all of index values separately
}

 

 

• map() method
• map() method calls the function once for each item in the array, passing in the item then adds the return value from each function call to a new array and returns the new array.

 function double(num) { 
      return num * 2 
 }

  const num = [1,2,3,4,5];
  const result = num.map(double);
  
  console.log(result); // [2,4,6,8,10]

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• filter() method
• Using filter() we can create new arrays with conditions below the array.
• filter() calls for every item in the array, if function is true then add to a new array.

 function isLong(name) { 
    return name.length > 3
    // get items legth more than 3
 }

 const arr = ["test", "abc", "apple", "it", "a"];
 const result = arr.filter(isLong);

 onsole.log(result);  // ['test', 'apple']

 

• split() method
• The split() method divides a string into a list of substrings and returns them as an array.
•  The split() method takes a single parameter, the character we want to separate.
• Also toString() converting an array to string
• Syntax :  string.split(separator, limit)

const message = "JavaScript::is::fun";

// divides the message string at ::

let result = message.split("::");
console.log(result);

// Output: [ 'JavaScript', 'is', 'fun' ]

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