how to change a value in an array of objects [duplicate]

Few comments for your code:

index = 4;
indexStates.filter(o => o[index] = !o[index]);

this 'index' should be a property name, not a position in the array, and with o[index] = !o[index] its a assignment, not a predicate

Instead, Try this

var indexStates = [ {"4": true}, {"3": false}, {"7": false}, {"1": true} ];
var index = 4;
var toChange = indexStates.filter(o => Object.getOwnPropertyNames(o).filter(n => n == index)[0] !== undefined)[0];
toChange[index] = !toChange[index]

console.log(toChange);
console.log(indexStates);

If you do not want to create a copy, you should go for for loop and check if the key/object exists int the current object and verify. If the value is there then negate it. Below is the snippet for the same. Hope this helps

const indexStates = [ {"4": true}, {"3": false}, {"7": false}, {"1": true} ];

index = "4";
const length = indexStates.length;

for(let i =0; i< length; i++) {
  let elem = indexStates[i];
  if(elem[index]) elem[index] = !elem[index]
}
console.log(indexStates);

If you can't make a copy of the array... then you could do this:

const getIndexOfTarget = (states, target) => {
  const value = states.find(state => Object.keys(state)[0] === target)
  return states.indexOf(value)
}

const states = [{"4": true}, {"3": false}, {"7": false}, {"1": true}];
const target = String(4)
const itemToChange = getIndexOfTarget(states, target)

states[itemToChange][target] = false // or !states[itemToChange][target]

Note I cast the index, or in this case target, to a String because that's what the key types are in the objects (you could just put "4" if you own it).

If you're going to have multiple "index" of the same value, then you'd need to swap the find with a filter.

const getIndexesOfTarget = (states, target) => {
  const values = states.filter(state => Object.keys(state)[0] === target)
  return values.map(val => states.indexOf(value))
}

const itemsToChange = getIndexesOfTarget(states, target)
itemsToChange.forEach(item => states[item][target] = !states[item][target])

I would go with a foreach approach

const indexStates = [ {"4": true}, {"3": false}, {"7": false}, {"1": true} ];

indexStates.forEach(elem => {
       if(typeof elem[index] === 'undefined') return elem;
       elem[index] = !elem[index];
       return elem;
    }

How about forEach. You can do it like this, if I understand your question correctly:

var indexStates = [ {"4": true}, {"3": false}, {"7": false}, {"1": true} ];
var target = '4';
indexStates.forEach(val=>{
    if(Object.keys(val).includes(target)) val[target]=!val[target];
});
console.log(indexStates);