JavaScript Linked List Example

Use a linked list with elements composed of two-part arrays. Each array has a current value and next pointer.

Linked list. In JavaScript we often build up an array of elements. Sometimes an algorithm may be helped by a linked list—less array resizing is needed.

With a two-element array, we can store a "current" value and "next" pointer. Then to loop over the linked list, we can access all the next pointers.

Example program. Let us begin. This program has a global variable called "list." This is an array of linked lists. Each "head" of a linked list is at an index in this list.

AddToList: This method adds an element at an index in the linked list. The current value (even if undefined) is placed as the "next" value.

Display: This loops over the pairs in the linked list at a certain index. It stops when an undefined "next" pointer is encountered.

JavaScript program that creates linked list var list = []; function addToList(n, value) { // Add to the list as this index. // ... Place existing entry as second element in a new array. // ... Replace current array. list[n] = [value, list[n]]; } function display(n) { // Loop over and display linked list. for (var pair = list[n]; pair; pair = pair[1]) { console.log("ITEM: " + pair[0]); } console.log("::END::"); } addToList(5, "cat"); addToList(5, "bird"); addToList(5, "frog"); addToList(1, "blue"); addToList(1, "green"); display(5); display(1); Output ITEM: frog ITEM: bird ITEM: cat ::END:: ITEM: green ITEM: blue ::END::

Some thoughts, performance. Usually an array is a better solution than a linked list. We can place many elements (thousands) into an array with no trouble.

However: For small lists, sometimes linked lists are a better option. No branches are needed to add an element.

For some programs, code size is most important. A linked list can be represented in only a few bytes of JavaScript. This can be an important advantage.

Avoid resizing arrays. This is not often a performance problem, but with linked lists we can avoid resizing arrays. And if we have existing objects we can reuse them for linking.Array

A summary. In most situations a linked list is not the best solution. But occasionally it can benefit a program: it may use less code and require less array resizing.

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JavaScript Linked List Example

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