javascript keep certain properties across objects in array

Question

I want to remove every attribute from objects in array except for some of them:

var listToKeep = ['name', 'school'];

var arrayOfObjects = [{id:'abc',name:'oh', school: 'a', sport: 'a'},
                      {id:'efg',name:'em', school: 'b', sport: 's'},
                      {id:'hij',name:'ge', school: 'c', sport: 'n'}]

I am trying with this, but this is only trying to remove one:

arrayOfObjects .forEach(function(v){ delete v.id});

the expected result will be:

var arrayOfObjects = [{name:'oh', school: 'a'},
                          {name:'em', school: 'b'},
                          {name:'ge', school: 'c'}]

i don't want to use for loop.

Answer 1

You can map each item in your array to new one, created by reducing list of keys to keep:

const newArray = arrayOfObjects.map(obj => listToKeep.reduce((newObj, key) => {
  newObj[key] = obj[key]
  return newObj
}, {}))

If you want to mutate original objects and delete properties, you can use two forEach loops and delete operator:

arrayOfObjects.forEach(obj => listToKeep.forEach((key) => {
  delete obj[key]
}, {}))

If you can use lodash or similar library, you can pick properties of object, e.g.:

const newArray = arrayOfObjects.map(obj => _.pick(obj, listToKeep))

Answer 2

You can loop over the keys of each JSON object in the arrayOfObjects array and then if the key is not found in the array listToKeep then remove that key:value from the object. And since you want to change the existing arrayOfObjects so you can follow this approach to use delete on the object property.

var listToKeep = ['name', 'school'];

var arrayOfObjects = [{id:'abc',name:'oh', school: 'a', sport: 'a'},
                      {id:'efg',name:'em', school: 'b', sport: 's'},
                      {id:'hij',name:'ge', school: 'c', sport:'n'}];
arrayOfObjects.forEach((obj)=>{
  Object.keys(obj).forEach((key)=>{
     if(listToKeep.indexOf(key) === -1){
       delete obj[key];
     }
  });
});
console.log(arrayOfObjects);