這兩個功能的相似之處在於它們都是不可分配的。

能具體解釋一下嗎？

在這篇文章中，我將分享它們之間的差異。

const 防止重新分配給變數。

在這種情況下，hisName 是一個不能重新分配的變數。

const hisName = 'Michael Scofield'

hisName = 'Lincoln Burrows'
// → ❌ Cannot assign to 'hisName' because it is a constant.

但是，您可以重新指派屬性。

const hisFamily = {
  brother: 'Lincoln Burrows'
}

hisFamily.brother = ''
// → ⭕️

hisFamily = {
  mother: 'Christina Rose Scofield'
}
// → ❌ Cannot assign to 'hisFamily' because it is a constant.

readonly 防止重新指派給屬性。

例如，如果嘗試用readonly給brother賦值，就會發生編譯錯誤。

let hisFamily: { readonly brother: string } = {
  brother: 'Lincoln Burrows'
}

hisFamily.brother = ''
// → ❌ Cannot assign to 'brother' because it is a read-only property.

另一方面，允許對變數本身進行賦值。

let hisFamily: { readonly brother: string } = {
  brother: 'Lincoln Burrows'
}

hisFamily = {
  brother: ''
}
// → ⭕️

結論

const 使變數本身不可分配，而 readonly 使屬性不可分配。

透過結合 const 和 readonly，您可以建立一個對象，其中變數本身和對象的屬性都是不可變的。

const hisFamily: { readonly brother: string } = {
  brother: 'Lincoln Burrows'
}

hisFamily.brother = ''
// ❌ Cannot assign to 'brother' because it is a read-only property.

hisFamily = {
  brother: ''
}
// ❌ Cannot assign to 'hisFamily' because it is a constant.

快樂編碼☀️