October 28, 1999 - Collections vs. Arrays
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October 28, 1999 Collections vs. Arrays  Tips: October 1999
Yehuda Shiran, Ph.D.
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Collection object is an object-oriented version of the Visual Basic array. Collection objects, like arrays, are containers for data. Like the elements in arrays, the members of collections can be accessed by their index value or their key. Unlike Visual Basic, collections in JavaScript are zero-based. That is, the index of the first item in the collection is 0. The most well-known collection in JavaScript is document.all, supported by Internet Explorer 4.0x and above.In JavaScript, collections don't have many advantages over arrays, because JavaScript is a loosely typed language. Given the similarity to arrays, why do we need collection objets? The major reason is ease of access and ease of maintenance:
- Members can be retrieved based on either their key value of their index value. The
item()method retrieves a member from the collection. - Members can be added before or after an existing member based on the laters index value. The
add()method adds a member to the collection. - Members can be deleted based on their index value. Multiple deletions, however, should be done backwards, from higher index values to lower ones, since the collection is reindexed after each deletion. The
remove()method deletes a member from the collection.
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