Why does `new Array(…[ 7 ])` produce `Array(7) [ <7 empty slots> ]`?

Why does this code print Array(7) [ <7 empty slots> ] (or an array of undefined, 7 times) instead of an array with the single element 7?

const a = [ 7 ];

console.log(new Array(...a));

>Solution :

new Array(…a) is the same as saying new Array(7), which will create an empty array with 7 undefined spots.