多选题

下列数组操作中，结果错误的有

Question

A.

let a = [1,2,3,4]

a.slice(0, 1)

// a: [1]

B.

let a = [1,2,3,4]

a.map(item => {

return item + 1

})

// a: [2,3,4,5]

C.

let a = [1,2,3,4]

a.splice(0, 1)

// a: [2,3,4]

D.

let a = [1,2,3]

let b = [4,5,6]

a.concat(b)

// a: [1,2,3,4,5,6] b:[4,5,6]