javascript - Why spread operator converts object param to one item array?

Question

"use strict";
let obj1 = { foo: 'bar', x: 42 };
function abc(...aaa) {
    console.log(aaa);
}
abc(obj1)
// log result: [{foo: 'bar', x: 42}]

"use strict";
let obj1 = { foo: 'bar', x: 42 };
function abc(...aaa) {
    console.log(aaa);
}
abc(obj1)
// log result: [{foo: 'bar', x: 42}]

question from:https://stackoverflow.com/questions/65862554/why-spread-operator-converts-object-param-to-one-item-array

Answer 1

This is not spread. These are rest parameters, which collect all remaining arguments passed into a single array.

Here, there's one argument, so using rest creates an array containing just that one argument (which happens to be an object).

Here are a couple other examples that might make it clearer:

function abc(...aaa) {
    console.log(aaa);
}
abc(5, 5, 5, 5, 5)
abc(3, 1, 2, 5)
abc(1, 2, 3)
abc(0)