how to replace a single key value pair from an object in react.js

Question

I have a single object of with key value pair, and i need to replace the first key value pair with a new key value in react.js. I have tried to make immutable process like

const data = {
   firstKey : firstValue,
   secondKey : secondValue,
   thirdKey : thirdValue
}

const newData = {...data, newFirstKey: newFirstValue}

but its adding a new key value pair to the object

You need to use the correct name of the first key it's firstKey not newFirstKey. Try const newData = {...data, firstKey: newFirstValue} — Mushroomator
– Mushroomator, Commented May 6, 2022 at 11:23
Because that's what the code does - it adds a new key/value pair to the object. Maybe just delete the old property? — Andy
– Andy, Commented May 6, 2022 at 11:24

Mushroomator · Accepted Answer · 2022-05-06 11:27:17Z

1

That is expected behavior. See MDN docs on spreading Objects.

If you want to replace a value you have to use the property name which you want to replace and set the new value.

const data = {
   firstKey : "firstValue",
   secondKey : "secondValue",
   thirdKey : "thirdValue"
}

const newData = {...data, firstKey: "newFirstValue"}
console.log(newData)

If you use a new unknown property name, this new property will be added to the object.

const data = {
   firstKey : "firstValue",
   secondKey : "secondValue",
   thirdKey : "thirdValue"
}

const newData = {...data, unknownProperty: "newFirstValue"}
console.log(newData)

answered May 6, 2022 at 11:27

Mushroomator

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