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# 4. Use ES6 Map class for storing the path tree

Date: 2020-06-01

# Status

Accepted

# Context

The Path tree is implemented using a nested key-value structure. Naturally a plain old Javascript object is ideal for this type of structure. However Javascript objects carry a lot of baggage from their prototype methods, which means they include properties that are set by default. As of ES6 Javascript provides a native class for key-value storage: Maps. This data structure overcomes the common problems with Javascript objects such as not including properties (or keys) that were not set explicilty, and is more memory efficient.

# Decision

Use ES6 Maps for consistent and efficient storage of the path tree.

# Consequences

Use the published API of Map to access and store the values.

However note that:

  • console.log and JSON.stringify are not straight forward any more, since they will not print the nested values
  • The keys or values are returned via an iterator, and as such forEach needs to be used, but map,reduce need the iterator first converted to Array (by array destructuring or any other method) first.

To overcome the above issues, toObject() and map() methods have been implemented to ease the process of printing out the tree and mapping the nodes to whatever data structure is needed.

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