js 値の操作_1

引数の初期値設定

function myfunc(price, tax = 0.1){
  const result = price + price * tax;
  return result;
}
myfunc(10); //11
myfunc(10, 0.08); //10.8

複数の引数を渡す

function myfunc(...numbers){
  let result = 0;
  for(const number of numbers){
    result += number;
  }
  return result;
}

反復処理のスキップ

//奇数だけ表示
for(let i = 0; i <10; i++){
  if(i % 2 === 0){
    continue;
  }
  console.log(i);
}

文字列のトリミング

const string1 = ' hello ';
string.trim(); //hello

文字列の操作

//文字列の検索
const mystring = 'javascript';
const string1 = mystring.indexOf('script'); //4
const string2 = mystring.indexOf('java'); //0
const string3 = mystring.lastIndex('a'); //3
const string4 = mystring.indexOf('html'); //-1
const string5 = mystging.search('script') //4

mystring.includes('script'); //true
mystring.startsWith('java'); //true
mystring.endsWith('script'); //true

//文字列を取り出す
mystring.slice(0,4); //java
mystring.slice(0); //javascript

mystring.substr(4,6); //script

//文字列の置き換え
const imageName = 'image1.png';
imageName.replace('1.png','2.png'); //images2.png

let phoneNumber = '080-1234-5678';
phoneNumber.replace('-', '');//0801234-5678
phoneNumber.replace(/-/g, '');//08012345678