i don’t understand the spread syntax in objects

The object spread is quite different. It maps to Object.assign() internally.

So const a = {...1} is same as const a = Object.assign({}, 1) Here Object.assign({},1) has treated 1 as object not as number. Therefore, you did not get any exception thrown.

Additionally if you have tried same thing for arrays [...1] it should have thrown error, since it does not treats 1 as object and you get the same behavior as ..1.

To summarize:

console.log({...false}) => console.log(Object.assign({}, false))
console.log({...1}) => console.log(Object.assign({}, 1))
console.log({...null}) => console.log(Object.assign({}, null))
console.log({...undefined}) => console.log(Object.assign({}, undefined))

PS: Object.assign() spec