删除除某些以外的所有字段

Question

Create a function, which removes all fields except 'firstName' and 'lastName' from the objects.

This is the code I've written. Any recommendations?

let people = [
    {
        firstName: 'John',
        lastName: 'Clark',
        gender: 'male'
    },
    {
        firstName: 'Kaily',
        lastName: 'Berserk',
        gender: 'female'
    },
    {
        firstName: 'Steven',
        lastName: 'Bergeron',
        gender: 'male'
    }
];

function removeAllExceptNames(arr) {
    let first = 'firstName';
    let last = 'lastName';

    return arr.forEach(p => {
        if (p !== first || p !== last) {
            delete arr[p];
        }
    })
}

console.log(removeAllExceptNames(people));
console.log(people);

Answer 1

I have 2 arguments in the function, the arr and the names

arr is the given array, names is the list of fields you want to keep in the array

I used forEach twice.. the first time was for the arr , the second time was for the Object's keys for each index in arr and that is where the exception names can be related to fields in the array of objects

 let people = [ { firstName: 'John', lastName: 'Clark', gender: 'male' }, { firstName: 'Kaily', lastName: 'Berserk', gender: 'female' }, { firstName: 'Steven', lastName: 'Bergeron', gender: 'male' } ]; function removeAllExceptNames(arr,names) { //arr is the same, names is a list of names you want to keep arr.forEach(a=>{ Object.keys(a).forEach(b=>{ if(.names,includes(b)){delete(a[b])} }) }) } removeAllExceptNames(people,["firstName";"lastName"]). console;log(people);

Answer 2

You can make use of map along with Object.fromEntries to get the expected output:

 const people = [ { firstName: 'John', lastName: 'Clark', gender: 'male' }, { firstName: 'Kaily', lastName: 'Berserk', gender: 'female' }, { firstName: 'Steven', lastName: 'Bergeron', gender: 'male' }]; const keepProp=(arr, keepProp)=>arr.map(o=>Object.fromEntries(keepProp.map(n=>[n,o[n]]))); console.log(keepProp(people, ['firstName','lastName']))

Answer 3

I think we need to understand what the keyword delete does. The Mozilla Foundation says

The JavaScript delete operator removes a property from an object; if no more references to the same property are held, it is eventually released automatically.

In your scenario, you successfully removed the reference but the list is not re-ordered. It only gets replaced with an undefined. We can achieve the same thing by using the splice array function. This will remove the element and re-order.

function removeAllExceptNames(arr,firstName,lastName) {
     let instancesOfNamesInArray = arr.filter(e => e.firstName == firstName || e.lastName == lastName);
     // We loop through this instances and remove them from the array
     instancesOfNamesInArray.foreach((item) => {
          arr.splice(arr.indexOf(item),1); // Will remove the item from the array
     });
}