1. 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

  2. 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

  3. 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