function generateRandomAlphaNum(len) {
  var rdmString = "";
  for (
    ;
    rdmString.length < len;
    rdmString += Math.random().toString(36).substr(2)
  );
  return rdmString.substr(0, len);
}

var numbers = [5, 458, 120, -215, 228, 400, 122205, -85411];
numbers = numbers.sort(function () {
  return Math.random() - 0.5;
});
/* the array numbers will be equal for example to [120, 5, 228, -215, 400, 458, -85411, 122205]  */

String.prototype.trim = function () {
  return this.replace(/^s+|s+$/g, "");
};

var array1 = [12 , "foo" , {name "Joe"} , -2458];

var array2 = ["Doe" , 555 , 100];
Array.prototype.push.apply(array1, array2);
/* array1 will be equal to  [12 , "foo" , {name "Joe"} , -2458 , "Doe" , 555 , 100] */

var argArray = Array.prototype.slice.call(arguments);

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

function isArray(obj) {
  return Object.prototype.toString.call(obj) === "[object Array]";
}

Array.isArray(obj); // its a new Array method

var numbers = [5, 458, 120, -215, 228, 400, 122205, -85411];
var maxInNumbers = Math.max.apply(Math, numbers);
var minInNumbers = Math.min.apply(Math, numbers);

var myArray = [12, 222, 1000];
myArray.length = 0; // myArray will be equal to [].

var items = [12, 548, "a", 2, 5478, "foo", 8852, , "Doe", 2154, 119];
items.length; // return 11
delete items[3]; // return true
items.length; // return 11
/* items will be equal to [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154,       119]   */

var items = [12, 548, "a", 2, 5478, "foo", 8852, , "Doe", 2154, 119];
items.length; // return 11
items.splice(3, 1);
items.length; // return 10
/* items will be equal to [12, 548, "a", 5478, "foo", 8852, undefined × 1, "Doe", 2154,       119]   */

var myArray = [12, 222, 1000, 124, 98, 10];
myArray.length = 4; // myArray will be equal to [12 , 222 , 1000 , 124].

myArray.length = 10; // the new array length is 10
myArray[myArray.length - 1]; // undefined

var foo = 10;
foo == 10 && doSomething(); // is the same thing as if (foo == 10) doSomething();
foo == 5 || doSomething(); // is the same thing as if (foo != 5) doSomething();

function doSomething(arg1) {
  arg1 = arg1 || 10; // arg1 will have 10 as a default value if it’s not already set
}

var squares = [1, 2, 3, 4].map(function (val) {
  return val * val;
});
// squares will be equal to [1, 4, 9, 16]

var num = 2.443242342;
num = num.toFixed(4); // num will be equal to 2.4432

0.1 + 0.2 === 0.3; // is false
9007199254740992 + 1; // is equal to 9007199254740992
9007199254740992 + 2; // is equal to 9007199254740994

for (var name in object) {
  if (object.hasOwnProperty(name)) {
    // do something with name
  }
}

var a =  0 ;
 var b = (a + , 99 );
 console . log (a);   // a will be equal to 1
console . log (b);   // b is equal to 99

var navright = document.querySelector("#right");
var navleft = document.querySelector("#left");
var navup = document.querySelector("#up");
var navdown = document.querySelector("#down");

isFinite(0 / 0); // false
isFinite("foo"); // false
isFinite("10"); // true
isFinite(10); // true
isFinite(undefined); // false
isFinite(); // false
isFinite(null); // true  !!!

var numbersArray = [1, 2, 3, 4, 5];
var from = numbersArray.indexOf("foo"); // from is equal to -1
numbersArray.splice(from, 2); // will return [5]

var person = { name: "Saad", age: 26, department: { ID: 15, name: "R&D" } };
var stringFromPerson = JSON.stringify(person);
/* stringFromPerson is equal to "{"name":"Saad","age":26,"department":{"ID":15,"name":"R&D"}}"   */
var personFromString = JSON.parse(stringFromPerson);
/* personFromString is equal to person object  */

var func1 = new Function(functionCode);
var func2 = eval(functionCode);

var sum = 0;
for (var i in arrayNumbers) {
  sum += arrayNumbers[i];
}

var sum = 0;
for (var i = 0, len = arrayNumbers.length; i < len; i++) {
  sum += arrayNumbers[i];
}

for (var i = 0; i < arrayNumbers.length; i++)

setInterval("doSomethingPeriodically()", 1000);
setTimeout("doSomethingAfterFiveSeconds()", 5000);

setInterval(doSomethingPeriodically, 1000);
setTimeout(doSomethingAfterFiveSeconds, 5000);

function getCategory(age) {
  var category = "";
  switch (true) {
    case isNaN(age):
      category = "not an age";
      break;
    case age >= 50:
      category = "Old";
      break;
    case age <= 20:
      category = "Baby";
      break;
    default:
      category = "Young";
      break;
  }
  return category;
}
getCategory(5); // will return "Baby"

function clone(object) {
  function OneShotConstructor() {}
  OneShotConstructor.prototype = object;
  return new OneShotConstructor();
}
clone(Array).prototype; // []

function escapeHTML(text) {
    var replacements= {"<": "&lt;", ">": "&gt;","&": "&amp;", """: "&quot;"};
    return text.replace(/[<>&"]/g, function(character) {
        return replacements[character];
    });
}

var object = ["foo", "bar"],
  i;
for (i = 0, len = object.length; i < len; i++) {
  try {
    // do something that throws an exception
  } catch (e) {
    // handle exception
  }
}

var object = ["foo", "bar"],
  i;
try {
  for (i = 0, len = object.length; i < len; i++) {
    // do something that throws an exception
  }
} catch (e) {
  // handle exception
}