Comments on a Breadth First Search Implementation

/**
* Let's think of the stations we can get to in one stop,
* she said. Then one stop from there. Spread like a stain.
* Like sunlight, until you fall on the end. You'll find
* the shortest way. Efficiently. The problem will grow.
* @param theMap changes every day, every minute, before your eyes,
* or we wouldn't need this
* @param start so we're here
* @param finish and we need to get there
* @returns not the path, but a tree, one stop to the next,
* and what came before
*/

function BreadthFirstSearch(theMap, start, finish){
// This poem would like permission
// to use your location. The price
// of always knowing where you are. Allow?
// Block? Add it to the list. Remember
let queue = [start];
// where you were before. Broadway-Lafayette.
// To Spring Street, those vacuum cleaners
// on display in the lobby. To 2nd Ave, Verkovena,
// tilted pool table like home. To West 4th stop,
// like Butterfly said. Before you began
let parents = new Array(theMap.length);
// cannot be undefined. The ontological argument. For
// convenience say God is just one less than zero.
parents[start]=-1;
// Until you get where you're going, or run out trying.
// Until Canarsie, Jamaican places
// had the veggie patties sometimes. To Coney Island,
// the jellyfish in uv light and the seals.
while(queue.length>0){
// Think of a line, like you're getting into PS1
// where Jeff danced in the fountain while we sipped
// wine and IPAs. It's just a fancy British word
// for the same thing. When you leave the museum
let current = queue.shift();
// Reach what you can touch.
for(let node of theMap[current]){
// Now I had a Boolean array here,
// but if you know where you came from
if(parents[node]===undefined){
// you've been there. If I walk down 3rd St.,
// it's like Tribes is still there. The Odeon,
// I can find for you no matter
// how long it's been.
parents[node]=current;
// it's like every step is the parent
// of the next.
queue.push(node);

if(node===finish){
// then you're there. Wherever you
// were supposed to go, the red pin where
// the interview, new apartment your lover
// and a cocktail. This is important,
// give back every step that got you there.
return parents;
}
}
}
}
// It can happen. Nothing returns. They all started out
// with bad directions.
throw "no path found";

}
/**
* Take me back. Every step. Forget the dead ends.
* Just the shortest path.
* @param previousStops every child knows nothing but what led to it.
* @param end We put his first, because we're going backward.
* @param start seems so long ago, doesn't it?
* @returns {Array} This is what you were looking for, the way.
* But it's too late you already did it.
*/
function traceBack(previousStops,end,start){
let next = end;
// In movies this happens when you die. I was conceived
// with the epoch. Two billion or so seconds
// is less than you think.
let path = [];
// Other languages would say 'pop'. In others,
// remembering the stop
// and forgetting it are two different operations. When memory
// is important. So much I forgot.
path.unshift(next);
do{
// Will I get to play this back
// from the beginning? Must I? You want to know
// what do we get? We only see so many moments
// out the window as the station rolls by.
// That's why movies fool us so easily.
next = previousStops[next];
// In San Francisco, you swipe to leave. What if
// you couldn't afford for life to let you go?
// Be thankful we can always get out here.
path.unshift(next);
} while (next!==start);
// Nothing written beyond this will happen. Forgive
// me and I'll forgive you. The rest is easy.
return path;
}