.once()

gun.once(callback)
gun.once(callback, options)

// Read user data once
gun.get('user/alice').once(function(data){
  console.log('Alice:', data)
})

// Read a specific property
gun.get('user/alice').get('name').once(function(name){
  console.log('Name:', name)
})

// Promisify .once() for async/await
function promiseOnce(gun) {
  return new Promise(function(resolve, reject){
    gun.once(function(data){
      resolve(data)
    })
  })
}

// Use with async/await
async function getUser() {
  var user = await promiseOnce(gun.get('user/alice'))
  console.log('User:', user)
  return user
}

// Data might not exist
gun.get('user/nonexistent').once(function(data){
  if(!data){
    console.log('User not found')
    return
  }
  console.log('User:', data)
})

// Read nested data
gun.get('user/alice').once(function(alice){
  console.log('Alice:', alice)
  
  // Read related data
  gun.get('user/alice').get('car').once(function(car){
    console.log('Alice\'s car:', car)
  })
})

// Wait longer for slow networks
gun.get('large/dataset').once(function(data){
  console.log('Data loaded:', data)
}, { wait: 500 })  // Wait 500ms instead of default 99ms

// Read all items from a set
gun.get('todos').map().once(function(todo){
  console.log('Todo:', todo)
})

// This calls .once() for each item in the set

function readIfExists(key) {
  gun.get(key).once(function(data){
    if(data === undefined){
      console.log(key + ' does not exist')
      return
    }
    console.log(key + ':', data)
  })
}

readIfExists('user/alice')
readIfExists('user/bob')

Gun.chain.once = function(cb, opt){
  opt = opt || {};
  if(!cb){ return none(this,opt) }
  var gun = this, cat = gun._, root = cat.root, data = cat.put, 
      id = String.random(7), one, tmp;
  gun.get(function(data, key, msg, eve){
    var $ = this, at = $._, one = (at.one||(at.one={}));
    if(eve.stun){ return } if('' === one[id]){ return }
    if(true === (tmp = Gun.valid(data))){ once(); return }
    if('string' == typeof tmp){ return }
    clearTimeout((cat.one||'')[id]);
    clearTimeout(one[id]);
    one[id] = setTimeout(once, opt.wait||99);
    function once(f){
      // ... handle data resolution and callback
      if(eve.stun){ return } if('' === one[id]){ return } one[id] = '';
      if(cat.soul || cat.has){ eve.off() }
      cb.call($, tmp, at.get);
      clearTimeout(one[id]);
    }
  }, {on: 1});
  return gun;
}

// If data is a link, .once() resolves it
gun.get('user/alice').get('car').once(function(car){
  // car is the actual car data, not a link reference
  console.log('Color:', car.color)
})

// For the link itself, use immediate read
var carLink = gun.get('user/alice').get('car')._

// ❌ Inefficient - multiple .once() calls
for(var i = 0; i < 100; i++){
  gun.get('items').get(i).once(function(item){
    console.log(item)
  })
}

// ✅ Better - use .map().once()
gun.get('items').map().once(function(item){
  console.log(item)
})

// Short wait for local/cached data
gun.get('cached/data').once(function(data){
  // Called within ~99ms
})

// Longer wait for remote/slow data
gun.get('remote/data').once(function(data){
  // Called within ~500ms or when data arrives
}, { wait: 500 })