JavaScript Patterns 2.3 For loops

HTMLCollections are objects returned by DOM methods such as:

• document.getElementsByName()

• document.getElementsByClassName()

• document.getElementsByTagName()

   

HTMLCollections, which were introduced before the DOM standard and are still in use today

document.images

All IMG elements on the page

document.links

All A elements

document.forms

All forms

document.forms[0].elements

All fields in the first form on the page

   

// used i+=1 instead of i++ to follow the rule of JSLint

for (var i = 0, max = myarray.length; i < max; i += 1) {

    // do something with myarray[i]

}  

• Use one less variable (no max)

• Count down to 0, which is usually faster because it's more efficient to compare to 0 than to the length of the array or to anything other than 0

The first modified pattern is:

var i, myarray = [];

for (i = myarray.length; i--;) {

    // do something with myarray[i]

} 

And the second uses a whileloop:

var myarray = [],
i = myarray.length;

while (i--) {

    // do something with myarray[i]

}