Why am I mutating the original array with filter method? [React]-CodePudding

After executing the newData[0].id = newValue I am actually updating the react initialData state. How is that possible?

Is my understanding that filter should return a new array different than the original one, also I am not ussing the setState feature so I don't understand why the state is changing.

CodePudding user response：

Because arrays are mutable. it will keep the reference to the original array even after filtering.

use the spread operator to avoid mutating the original array

const data = [...newData]
data[0].id = newValue

CodePudding user response：

As per the new beta docs on updating items in array

setInitialData(prev => {
 // create a new array
 const withReplaced = prev.map(elem => {

    if (elem.id === id) {
        const newVal = //set new value
        // create a new updated element
        return {
          ...elem,
          id: newVal
        }
      } else {
        // The rest haven't changed
        return elem;
      }

  });

 return  withReplaced;

})

Hope it helps

CodePudding user response：

you can't update the initialData,but the you can update the son of the array.And if you don't use "setData".The views won't change.