mempool: add/fix comments

lib/mempool/mempool.js

@@ -78,20 +78,29 @@ class Mempool extends EventEmitter {
     this.tip = this.network.genesis.hash;
     this.nextState = this.chain.state;
 
-    this.waiting = new BufferMap();
-    this.orphans = new BufferMap();
-    this.map = new BufferMap();
-    this.spents = new BufferMap();
-    this.claims = new BufferMap();
-    this.airdrops = new BufferMap();
-    this.airdropIndex = new Map();
-    this.claimNames = new BufferMap();
+    // "The" mempool
+    this.map = new BufferMap();      // hash -> MempoolEntry
+    this.claims = new BufferMap();   // hash -> ClaimEntry
+    this.airdrops = new BufferMap(); // hash -> AirdropEntry
+
+    // Orphans and missing parents
+    this.waiting = new BufferMap();  // parent hash -> BufferSet[spender hashes]
+    this.orphans = new BufferMap();  // orphan tx hash -> Orphan
+
+    // Prevent double-spends
+    this.spents = new BufferMap();     // prevout key -> MempoolEntry of spender
+    this.claimNames = new BufferMap(); // namehash -> ClaimEntry
+    this.airdropIndex = new Map();     // airdrop position -> AirdropEntry
+
+    // Track namestates to validate incoming covenants
+    this.contracts = new ContractState(this.network);
+
+    // Recently rejected txs by hash
     this.rejects = new RollingFilter(120000, 0.000001);
 
+    // Extensions of blockchain indexes by tx hash for API
     this.coinIndex = new CoinIndex();
     this.txIndex = new TXIndex();
-
-    this.contracts = new ContractState(this.network);
   }
 
   /**
@@ -3123,7 +3132,7 @@ class Orphan {
    * Create an orphan.
    * @constructor
    * @param {TX} tx
-   * @param {Hash[]} missing
+   * @param {Number} missing
    * @param {Number} id
    */