Good afternoon, I have this little program:
let oi=[1,2,3,4]
let xau=[]
xau=oi
xau[2]=7
console.log(oi)
My problem is that when in the console the output is:
[1,2,7,4]
According to what I understand, xau should be a new instance that has the values of hi, but when modifying xau, tbm modifico hi, if someone can explain to me why this is happening and how do I can modify xau without modifying hi, I am grateful
In Javascript, arrays and objects are passed by reference. So you can edit the values of the array oi through the variable xau , since both point to the same array.
You can create a copy of the oi array and assign it to xau using the .slice .
let oi=[1,2,3,4]
let xau=oi.slice()
xau[2]=7
console.log(oi, xau) Another way is to use .map() :
let oi=[1,2,3,4]
let xau = oi.map(Number)
xau[2]=7
console.log(oi, xau) The .map() will generate a new independent array with the oi values.
The problem has already been explained by @PanterA, but to stay as a reference to future readers I leave here another way to create a copy of the array using concat :
let xau = oi.concat()
The concat serves to concatenate the array with what is passed by parameter. Nothing happens but only the original array.
Example:
let oi=[1,2,3,4]
let xau=oi.concat()
xau[2]=7
console.log(oi, xau)Using ES6 and spread operator can make the copy even simpler with:
let xau = [...oi]
See it working:
let oi=[1,2,3,4]
let xau= [...oi]
xau[2]=7
console.log(oi, xau)