How Can I? Iterate Through the Keys of an Object with a Statement

Tell us what’s happening:
My code logs each instance of the condition being true, but I don’t know how to mutate this information to return a sum…

Your code so far

let users = {
  Alan: { age: 27, online: false },
  Jeff: { age: 32, online: true  },
  Sarah:{ age: 48, online: false },
  Ryan: { age: 19,online: true }

function countOnline(obj) {
  // change code below this line
let prop = 'online'
for (let x in obj) {
  if (obj[x][prop] === true){
  // change code above this line

//Returns true true

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Link to the challenge:

You need to create an accumulator and increment it where you are currently logging to the console.