[자바스크립트] 8.배열

 

  //8. 배열 array

            //1. Declaration

            const arr1 = new Array();

            const arr2 = [1,2];

 

            //2. index position

            const fruits = ['apple', 'banana'];

            console.log(fruits);

            console.log(fruits.length);

            console.log(fruits[0]);

            console.log(fruits[1]);

            console.log(fruits[2]);//undefined

            console.log(fruits[fruits.length-1]);

 

            //a. for

            for(let i = 0 ; i<fruits.length ; i++){

                console.log(fruits[i]);

            }

 

            //b. for of

            for(let fruit of fruits){

                console.log(fruits[fruit]);

            }

 

            //c. foreach

            fruits.forEach(function(fruit, index, array){

                console.log(fruit, index, array);

            })

 

            //anonymous함수 일 때

            fruits.forEach((fruit) =>console.log(fruit));

 

            //d. Addition, deletion, copy

            

            //push: add an item to the end

            fruits.push("strawberry","peach");

            console.log(fruits);

            

            //pop: remove an item from the end

            fruits.pop();

            fruits.pop();

            console.log(fruits);

            

            //unshift: add an item to the beginnig

            fruits.unshift("strawberry","lemon");

            console.log(fruits);

 

            //shift: remove an item from the beginning

            fruits.shift();

            fruits.shift();

            console.log(fruits);

 

            //note!! shift, unshift are slower than pop, push

            //뒤에서 시작하면 뒤에만 빼고 빠지면됨.

            //앞에서 빼거나 추가하면 index가 움직여야하므로 느림. (전체의 데이터가 움직임)

 

            //splice: remove an item by index position

            fruits.push('strawberry','peach','lemon');

            console.log(fruits);

            fruits.splice(1,2);//인자를 하나만 쓰면 그 index부터 뒤에 다 지움

            console.log(fruits);

            fruits.splice(1,1,'tangerine','pear');//지운거 사이에들어감.1번쨰부터 1개를 지우고서 그 사이에 귤, 배 들어감

            console.log(fruits);

 

            //combine two arrays;

            const fruits2=['pear','coconut'];

            const newFruits = fruits.concat(fruits2);

            console.log(newFruits);

 

            //5. Searching

            //find the index

            console.clear();

            console.log(fruits);

            console.log(fruits.indexOf('apple'));

            console.log(fruits.indexOf('pear'));

            

            //includes

            console.log(fruits.includes('pear'));//true

            console.log(fruits.indexOf('coconut')); //-1 (없을때)

 

            //lastIndexOf

            console.clear();

            fruits.push('apple');

            console.log(fruits);

            console.log(fruits.indexOf('apple'));//가장앞에있는 0출력

            console.log(fruits.lastIndexOf('apple')); //마지막에있는 apple index 4 출력