Code Kata: Using Array Reduce() To Navigate An Object Graph In JavaScript

reduce.js

// I am just an arbitrarily non-trivial object to query.
var config = {
	tasks: {
		interval: {
			//...
		},
		daily: {
			backupFilesToS3: {
				dayOfWeek: "Saturday",
				hour: 22
			}
		}
	}
};


// Now, imagine that we are given an object query that is a dot-delimited path of
// object navigation instructions. And, we want to find the value that resides at
// the end of this path.
var objectQuery = "tasks.daily.backupFilesToS3.dayOfWeek";

var value = objectQuery
	// To find the value, we can split the query / object-path on the dot-operator and
	// treat each token as a single object-property navigation instruction.
	.split( "." )

	// With the resultant array of navigation tokens, we can then reduce the set of
	// steps down to the target value by using the reduction's "previousValue" as our
	// place-holder in the object graph. Essentially, each step of the reduce() operation
	// takes us one level deeper into the object graph, returning the result of a single
	// step in the object path.
	.reduce(
		function iterator( previousValue, navigationToken ) {

			// If the previous navigation was successful, return the result of the NEXT
			// step in set of navigation operations. Otherwise, return the failed result
			// of the previous navigation.
			return( previousValue && previousValue[ navigationToken ] );

		},
		config // ... starting at the root of the object graph.
	)
;

console.log( "Query Result:", value );


// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //


// And, of course, there's the old-school way to just evaluate the code :D Which is
// likely to throw red-flags by your team's linting system and code-review process.
console.log( "EVAL Query Result:", eval( "config." + objectQuery ) );

Nice 👍 I was able to get as far as tokens for each of the . parts, but converting that to traversing the object graph was where I got stuck (I was heading towards a for/while loop and the array shift method, but really like elegance of your solution).