https://leetcode.com/problems/stream-of-characters/submissions/

streamOfChars.js

var StreamChecker = function(words) {    
    this.tree = PrefixTree();
    this.maxWordLength = 0;
    words.forEach((word) => {
        this.tree.add(word.split('').reverse().join(''));
        this.maxWordLength = Math.max(this.maxWordLength, word.length);
    });
    this.storage = []; // should be a queue! This is O(n) time as opposed to a queues O(1)
};

StreamChecker.prototype.query = function(letter) {
    if(this.storage.length === this.maxWordLength) this.storage.shift();
    this.storage.push(letter);
    return this.tree.has(this.storage.length-1, this.storage);
};

const PrefixTree = () => {
  
    const self = {
        children: {}, // could use map but this has shorter syntax
        terminal: false
    };

    
    self.add = (word) => {
        if(!word.length){
            self.terminal = true;
            return;
        }
        const prefix = word[0];
        const suffix = word.slice(1);
        if(!self.children.hasOwnProperty(prefix)) self.children[prefix] = PrefixTree();
        self.children[prefix].add(suffix);
    };

    self.has = (index, storage, log=false) => {
        if(self.terminal) return true;
        if(index < 0) return false;      
        const prefix = storage[index];
        if(!self.children.hasOwnProperty(prefix)) return false;
        return self.children[prefix].has(index-1, storage, log);
    };
    
    
    return self;
};