Why use spread operator to merge two arraies then report an Unexpected token?

Question

this is my code:

let arrA = [1,2,3]
let arrB = [3,4,5,6]
let result = []
//  error: Unexpected token
[...arrA,...arrB].forEach(item => {
  if(arrA.includes(item)&&!arrB.includes(item)) result.push(item)
})
console.log(result)

but this work well

Array.from([...arrA,...arrB]).forEach(item => {
  if(arrA.includes(item)&&!arrB.includes(item)) result.push(item)
})

how does it comes?