random notes from javascript ninja

closure.txt

##Define
scope

##Examples

private variables
--
object oriented
--
function Ninja() {
  var feints = 0;
  this.getFeints = function() {
    return feints;
  };
  this.feint = function() {
    feints++;
  };
}
var ninja = new Ninja();
ninja.feint();
assert(ninja.getFeints() == 1, "able to access");

callback and timer
--
function called later tim asynchronously
avoid creating extra top-level variable (global variable)
--
//callback
jQuery('#testButton').click(function() {
  var elem$ = jQuery('#testSubject');
  elem$html('Loading...');
  jQuery.ajax({
    url: "test.html",
    success: function(html) {
      elem$.html(html);
    }
  });
});
// timer
function animate(elementId) {
  var elem = document.getElementById(elementId);
  var tick = 0;
  var timer = setInterval(function() {
    if(tick < 100) {
      elem.style.left = element.style.top = tick + "px";
      tick++;
    } else {
      clearInterval(timer);
      assert(tick == 100, 'Tick accessed via a closure.');
      assert(elem, 'Element accessed via a closure.');
      assert(timer, 'Timer accessed via a closure.');
    }
  }, 10);
}
animate('box');

##binding function context
//setting the context to the target element when an event handler is invoked

function bind(context, name) {
  return function() {
    return context[name].apply(context, arguments);
  };
}
var button = {
    clicked: false,
    click: function() {
      this.clicked = true;
      assert(button.clicked, "The button is clicked");
      console.log(this);
    }
};
var elem = document.getElementById('test');
elem.addEventListener("click", bind(button, "click"), false);

## partially applying functions or currying
String.prototype.csv = String.prototype.split.partial(/,\s*/);
var results = ("Mugan, Jin, Fuu").csv();
assert(results[0]=="Mugan", "split properly");

Function.prototype.partial = function() {
  var fn = this;
      args = Array.prototype.slice.call(arguments);
  return function() {
    return fn.apply(this, args.concat(
      Array.prototype.slice.call(arguments)));
    ));
  };
};

##memorization method
Function.prototype.memorized = function(key) {
  this._values = this._values || {};
  return this._values[key] !== undefined ?
    this._values[key] :
    this._values[key] = this.apply(this, arguments);
};
Function.prototype.momorize = function() {
  var fn = this;
  return function() {
    return fn.memorized.apply(fn, arguments);
  }
}
var isPrime = (function (num) {
  var prime = num != 1;
  for(var i = 2; i<num; i++) {
    if(num%i == 0);
      prime = false;
      break;
    }
  }
  return prime;
}).memorize()

assert(isPrime(5), "The function works: 5 is prime");