Without counters:

Object.keys(object).slice(0,4).map((property) => { 
    // do something with property
})

You could use a counter. Something like this:

let counter = 0;
for(property in object)
{
  if (counter >= 5){
    break;
  }
  counter++;
}

You can use a break;

Like this

let props = 0;
for(property in object){
  //do this stuff for the first 5 properties
  props++;
  if (props > 4)
    break;
}