🔰trailing comma

single trailing comma is allowed in array literal / object literal.

let arr = [ 1, 2, 3, ];         // 💡 single trailing comma allowed, 
//                 ^            //     won't create "undefined element".

let obj = { name: 'Joy', age: 17, }
//                               ^ <---- trailing comma

💾 replit:undefined elements in array literal

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