Reduce of empty array with no initial value

demo https://codepen.io/gnjo/pen/XQjrqX?editors=1010

let a=[],b=['xxx'],c=['ee'],d=void 0
;
let ret=[].reduce((a,b)=>a.concat(b),[]) //safe
console.log(ret)
let ret2=[].reduce((a,b)=>a.concat(b)) //Reduce of empty array with no initial value
console.log(ret2)
let ret3=[a,b,c,d].reduce((a,b)=>a.concat(b))
console.log(ret3)
;//