デフォルト引数
function fn(arg) { arg = typeof arg === 'undefined' ? 0 : arg; return ++arg; } console.log(fn()); //=> 1 console.log(fn(0)); //=> 1 console.log(fn(1)); //=> 2
function fn(arg) { arg = typeof arg === 'undefined' ? 0 : arg; return ++arg; } console.log(fn()); //=> 1 console.log(fn(0)); //=> 1 console.log(fn(1)); //=> 2