Read the original article here
There are two ways to create, update, and delete items to an array in JavaScript. The first approach is by using the destructive methods which will change the object itself.
The second approach is by using the immutable methods, which will return a new array that contains a new updated value. This could be very useful if your using Redux or any other state management library.
Let's say we have an array contains a some items like below.
const list = ["Item 1", "Item 2", "Item 3"]
Create item
The mutable way:
const newItem = "Item 4"
list.push(newItem)
The immutable way:
const newItem = "Item 4"
const newList = list.concat([newItem])
Result:
[
"Item 1",
"Item 2",
"Item 3",
"Item 4"
]
Update item
The mutable way:
const itemIndex = 1
const newItem = "Item 2 (updated)"
list[itemIndex] = newItem
The immutable way:
const itemIndex = 1
const newItem = "Item 2 (updated)"
const newList = list.map((item, index) => {
return index === itemIndex ? newItem : item
})
Result:
[
"Item 1",
"Item 2 (updated)",
"Item 3"
]
Delete item
The mutable way:
const itemIndex = 1
list.splice(itemIndex, 1)
The immutable way:
const itemIndex = 1
const newList = list.filter((item, index) => {
return index !== itemIndex
})
Result:
[
"Item 1",
"Item 3"
]
Top comments (6)
I think there is a typo in your immutable create example.
You've switched the name of the variable of the initial array from
listtostateFixed 👌, thanks for pointing out a problem!
Nice post 👍
Thanks!
If those are JavaScript statements, they need to end in a semicolon.
Not necessarily - it's definitely useful for code clarity, but in JS many statements are implicitly terminated by a newline. The StandardJS style guide omits them when not explicitly necessary.