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function countAllCharacters(str) { | |
let obj = {}; | |
for(let i = 0; i < str.length; i++){ | |
if (obj[str[i]] === undefined) { | |
obj[str[i]] = 0 | |
} | |
obj[str[i]]++ | |
} | |
return obj; | |
} |
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function countAllLetters(str) { | |
let obj = {}; // 변수에 빈 객체 할당 | |
for(let i = 0; i < str.length; i++){ // 반복문을 통해 인자로 받은 문자열 순회 | |
if (obj[str[i]] === undefined) { // i번째 문자가 기존 객체의 키로 존재하지 않으면 | |
obj[str[i]] = 0 // i번째 문자와 0을 새로운 키값으로 생성 | |
} | |
obj[str[i]]++ // 해당 문자가 반복될 때 마다 1씩 값을 추가한다. | |
} | |
return obj; | |
} |
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// 문자열을 입력받아 문자열을 구성하는 각 문자를 키로 갖는 객체를 리턴 | |
let output = countAllLetters('apple'); | |
console.log(output); // --> {a: 1, p: 2, l: 1, e: 1} |
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console.log(score); // undefined | |
var core; // 변수 선언문 |
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function foo() { | |
return; | |
{ | |
} | |
// ASI의 동작 결과 => return; {}; | |
// 개발자의 예측 => return {}; | |
} | |
console.log(foo()); // undefined |
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console.log(10 / 0); //Infinity | |
console.log(10 / -0); //-Infinity | |
console.log(1 * "string"); // NaN |
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var first = "Hyeon-jun"; | |
var last = "Moon"; | |
// ES5 : 문자열 연결 | |
console.log("My name is " + first + "" + last + "."); | |
// My name is Hyeon-jun Moon. |
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5 + 2; // 7 | |
5 - 2; // 3 | |
5 * 2; // 10 | |
5 / 2; // 2.5 | |
5 % 2; // 1 |
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// ++ 연산자는 피연산자의 값을 변경하는 암묵적 할당이 이뤄진다. | |
x++; // x = x + 1; | |
console.log(x); // 2 | |
// -- 연산자는 피연산자의 값을 변경하는 암묵적 할당이 이뤄진다. | |
x--; // x = x - 1; | |
console.log(x); // 1 |
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// 동등 비교 | |
5 == 5; // true | |
// 타입은 다르지만 암묵적 타입 변환을 통해 타입을 일치시키면 동등하다. | |
5 == "5"; // true |
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