TypeScript SpellChecker

export interface IChecker {
    check: (word: string) => boolean;
};

export interface ClumsyEntry {
    valid: boolean;
    children: ClumsyEntries;
}

export interface ClumsyEntries {
    [letter: string]: ClumsyEntry;
}

export interface ClumsyStats {
    letters: number;
    nodes: number;
    words: number;
}

export class ClumsyChecker implements IChecker {
    tree: ClumsyEntry = {valid: false, children: {}};
    stats: ClumsyStats = {letters: 0, nodes: 1, words: 0};

    add (word: string): void {
        var node = this.tree;
        for (var i = 0; i < word.length; i++) {
            var letter = word[i].toLowerCase();
            if (!node.children[letter]) {
                node.children[letter] = {valid: false, children: {}};
                this.stats.nodes += 1;
            }
            node = node.children[letter];
            node.valid = (i == word.length - 1) || node.valid;
            this.stats.letters += 1;
        }
        this.stats.words += 1;
    }

    check (word: string): boolean {
        var node = this.traverse(word);
        if (node === null) {
            return false;
        } else {
            return node.valid;
        }
    }

    private traverse (word: string): ClumsyEntry {
        var node = this.tree;
        for (var i = 0; i < word.length; i++) {
            var letter = word[i].toLowerCase();
            if (!node.children[letter]) {
                return null;
            } else {
                node = node.children[letter];
            }
        }
        return node;
    }
};