【JavaScript】数値範囲による分岐2 - Qiita

//Object.entriesだけでも動作はする const generations = new Map(Object.entries({ 12: 'under 12', 20: 'teenager', 30: '20s', 40: '30s', 50: '40s', 60: '50s', 70: '60s', 80: '70s', 90: '80s', 100: '90s', })); const getGeneration = age => { if (!Number.isFinite(age) || age < 0) return; for (const [key, value] of generations) { if (age < key) return value; } return 'over 100'; }; console.log( getGeneration(-1)