JavaScript: prototype property

In JavaScript, prototype is a property of functions which easily allows for object extension and inheritance.

var x = {};
x.prototype; // undefined

x = [];
x.prototype; // undefined

x = function(){};
x.prototype; // Object

To extend an object with prototype:

Array.prototype.add = function() {
  var length = this.length;
  var sum = 0;
  for (var i = 0; i < length; i++) {
    if (!isNaN(this[i])) {
      sum += this[i];
    }
  }
  return sum;
};

[2, 3, 5, 'ha ha ha ha', 10].add(); //20

The above serves as an example. Do not extend native objects lightly. This topic is discussed extensively at javascriptweblog.

To inherit from an object with prototype:

var Parent = function() {
  this.name = 'parent';
  this.getName = function() {
    return this.name;
  };
};

var Child = function() {
  this.name = 'child';
};

Child.prototype = new Parent();
Child.prototype.constructor = Child;

var p = new Parent();
p.getName(); // 'parent'

var c = new Child();
c.getName(); // 'child'

Child.prototype.actChildish = function() {
  // childish behavior
};

c.actChildish();

p.actChildish(); // error

Note that updating Child’s prototype to include actChildish updates the already instantiated object c and that p did not get actChildish added to its prototype.

JavaScript:

  jQuery === $;
  // true

JavaScript:

  undefined = 10;

  typeof undefined; // 'number'
  undefined === 10 // true

Regex:

[ \t]+$

Replace with “” to remove trailing whitespace from a file.

JavaScript: test if a property is a function

  var isFunction = function(property) {
    return typeof property === 'function';
  }

  var x = {
    qq : 'QQ'
  };

  x.doStuff = function() {
    "stuff happened";
  };

  console.log(isFunction(x.doStuff)); // true
  console.log(isFunction(x.hasOwnProperty)); // true
  console.log(isFunction(x.qq)); // false

JavaScript Type Coercion

JavaScript:

  2 + "256" // "2256"
  2 - "256" // -254

  typeof (+"256") // number
  typeof (-"256") // number

  2 + +"256" // 258
  2 - -"256" // 258

  typeof -"" // number
  typeof +"" // number

  +"" === -"" // true
  +"" === 0 // true
  "" === 0 // false

JavaScript: isInt function

  var isInt = function(x) {
    return x === parseInt(x, 10) && !isNaN(x);
  }

  console.log(isInt(755)); // true
  console.log(isInt(-644)); // true
  console.log(isInt(0)); // true
  console.log(isInt(3.14)); // false
  console.log(isInt("256")); // false
  console.log(isInt("-256")); // false
  console.log(isInt("7.62")); // false
  console.log(isInt("-0.14")); // false
  console.log(isInt(true)); // false
  console.log(isInt("false")); // false
  console.log(isInt("I'm singin' in the rain")); // false
  console.log(isInt({})); // false
  console.log(isInt([])); // false
  console.log(isInt(undefined)); // false
  console.log(isInt(null)); // false