JavaScript foreach Vs for

var myArray = [{'key': 'value'}, {'key': 'value1'}];

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

for (var i in myArray)

for (var i = 0; i < a.length; i++)
   //do stuff with a[i]

for (var key in o)
  //do stuff with o[key]

for(name in object)
{
    if (object.hasOwnProperty(name))
    {
    }
}

$(['a','b','c']).each(function() {
    alert(this);
});
//Outputs "a" then "b" then "c"

for (var i = myArray.length-1; i >= 0; i--)

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

l = ''; for (m in obj) { l += m + ' => ' + obj[m] + 'n' } console.log(l);

var array = [0, 1, 2, , , 5];

for (var k in array) {
  // Not guaranteed by the language spec to iterate in order.
  alert(k);  // Outputs 0, 1, 2, 5.
  // Behavior when loop body adds to the array is unclear.
}

for (var i = 0; i < array.length; ++i) {
  // Iterates in order.
  // i is a number, not a string.
  alert(i);  // Outputs 0, 1, 2, 3, 4, 5
  // Behavior when loop body modifies array is clearer.
}

function foreach(o, f) {
 for(var i = 0; i < o.length; i++) { // simple for loop
  f(o[i], i); // execute a function and make the obj, objIndex available
 }
}

foreach(o, function(obj, i) { // for each obj in o
  alert(obj); // obj
  alert(i); // obj index
  /*
    say if you were dealing with an html element may be you have a collection of divs
  */
  if(typeof obj == 'object') {
   obj.style.marginLeft = '20px';
  }
});

for( var i=0,j=null; j=array[i++]; foo(j) );