let c = null let val = a || 'not found' // val = 'not found' val = b || 'not found' // val = 'not found' val = c || 'not found' // val = 'not found' Null演算子 let a = '' let b = 0 let c = null let val = a ?? 'not found' // val = '' val = b ?? 'not found' // val = 0 val = c ?? 'not found' // val = 'not found'