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Help us understand the problem. What are the problem?

posted at

updated at

JavaScript

1、boolean型
boolean型と=trueかfalseを代入できる変数の事。

let b = false;
if(b){
console.log('はい');
}else{
console.log('いいえ');
}
出力結果→いいえ

console.log(b); →false
console.log(!b); →true

2、論理演算子

&& 論理AND=AとBがあったら両方trueの場合trunを返す
console.log(true && true);  →true
console.log(true && false);  →false
console.log(false && true);  →false
console.log(false && false); →false

||論理OR=論理値AとBがあったらどちらかがtrueの場合trueを返す
console.log(true || true);  →true
console.log(true || false);  →true
console.log(false || true);  →true
console.log(false || false); →false

!論理NOT=論理値を反転させる
console.log(!true); →false
console.log(!false); →true

優先順位
! && ||
console.log(false && true || true); →true
console.log(false && (true || true)) →false

3、nullとundefined

//undefined
let x;
console.log(x); →undefined

let item = y;

4、三項演算子

//条件式? trueの場合:falseの場合
(例題)
let score = 70;
let judgement = (score > 50) ? '合格' : '不合格';
console.log(judgement); →合格

5、コールバック関数

function greeting(name){
console.log('Hello' + name + '-san');
}

function inputUserName(callback){
let name = prompt('あなたの名前を入力してください');  
callback(name);
}

inputUserName(greeting); 

6、配列

let colors = ['red','green','blue'];
console.log(colors);  →全ての配列を出力 red,green,blue
console.log(colors[0]); →1つ目の配列を出力 red

//個数
console.log(colors.length); →3


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Help us understand the problem. What are the problem?