JavaScript の once よくつかうので (I actually don't use it that often)

once.js

function once (fn) {
  var done = false, result;
  function _once_ () {
    if(!done) {
      result = fn.apply(this,Array.prototype.slice.call(arguments))
      done = true;
    }
    return result;
  }
  return _once_;
}

test.js

// Test object style:

function TestObject(prop) {
  this.setProp = function(newProp) {
    prop = newProp;
    return prop;
  }
  this.getProp = function() {
    return prop;
  }
}

(function(){

  var t = new TestObject(5);
  console.log('getProp start',t.getProp());
  t.setPropOnce = once(t.setProp);
  console.log('setPropOnce(11) first time',t.setPropOnce(11));
  console.log('setPropOnce(13) second time',t.setPropOnce(13));
  console.log('getProp end',t.getProp());

})();


console.log('-----------');

// Test functional style:

(function(){
  
  var x = 0;
  function t(y) {
    x += y;
    return x;
  }
  
  var tOnce = once(t);
  
  console.log('x start',x);
  console.log('tOnce(3) first time',tOnce(3));
  console.log('tOnce(5) second time',tOnce(5));
  console.log('x end',x);
  
})();

See also the same function in underscore.js https://github.com/documentcloud/underscore/blob/3b023262ce795083fa37777f4846209cc7fe33e7/underscore.js#L630
They clear the function reference after calling it once.