diff --git a/assembly/decoder.ts b/assembly/decoder.ts
index 1e6eec4..07c16e4 100644
--- a/assembly/decoder.ts
+++ b/assembly/decoder.ts
@@ -1,6 +1,3 @@
-declare function logStr(str: string): void;
-declare function logF64(val: f64): void;
-
 /**
  * Extend from this class to handle events from parser.
  * Default implementation traverses whole object tree and does nothing.
@@ -76,8 +73,8 @@ let CHAR_A_LOWER = "a".charCodeAt(0);
 
 export class DecoderState {
     readIndex: i32 = 0;
-    buffer: Uint8Array = null;
-    lastKey: string = null;
+    buffer: Uint8Array = new Uint8Array(0);
+    lastKey: string | null = null;
 }
 
 export class JSONDecoder<JSONHandlerT extends JSONHandler> {
@@ -89,7 +86,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
         this.handler = handler;
     }
 
-    deserialize(buffer: Uint8Array, decoderState: DecoderState = null): void {
+    deserialize(buffer: Uint8Array, decoderState: DecoderState = null as DecoderState): void {
         if (decoderState) {
             this.state = decoderState;
         } else {
@@ -123,7 +120,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
             || this.parseString()
             || this.parseBoolean()
             || this.parseNumber()
-            || this.parseNull()
+            || this.parseNull();
         this.skipWhitespace();
         return result;
     }
@@ -132,7 +129,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
         if (this.peekChar() != "{".charCodeAt(0)) {
             return false;
         }
-        let key = this.state.lastKey;
+        let key = this.state.lastKey as string;
         this.state.lastKey = null;
         if (this.handler.pushObject(key)) {
             this.readChar();
@@ -165,7 +162,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
         if (this.peekChar() != "[".charCodeAt(0)) {
             return false;
         }
-        let key = this.state.lastKey;
+        let key = this.state.lastKey as string;
         this.state.lastKey = null;
         if (this.handler.pushArray(key)) {
             this.readChar();
@@ -183,21 +180,21 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
             assert(this.readChar() == "]".charCodeAt(0), "Unexpected end of array");
         }
         this.handler.popArray();
-        return true;;
+        return true;
     }
 
     private parseString(): bool {
         if (this.peekChar() != '"'.charCodeAt(0)) {
             return false;
         }
-        this.handler.setString(this.state.lastKey, this.readString());
+        this.handler.setString(this.state.lastKey as string, this.readString());
         return true;
     }
 
     private readString(): string {
         assert(this.readChar() == '"'.charCodeAt(0), "Expected double-quoted string");
         let savedIndex = this.state.readIndex;
-        let stringParts: Array<string> = null;
+        let stringParts: Array<string> = null as Array<string>;
         for (;;) {
             let byte = this.readChar();
             assert(byte >= 0x20, "Unexpected control character");
@@ -231,8 +228,6 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
                 savedIndex = this.state.readIndex;
             }
         }
-        // Should never happen
-        return "";
     }
 
     private readEscapedChar(): string {
@@ -301,7 +296,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
             digits++;
         }
         if (digits > 0) {
-            this.handler.setInteger(this.state.lastKey, number * sign);
+            this.handler.setInteger(this.state.lastKey as string, number * sign);
             return true;
         }
         return false;
@@ -310,12 +305,12 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
     private parseBoolean(): bool {
         if (this.peekChar() == FALSE_STR.charCodeAt(0)) {
             this.readAndAssert(FALSE_STR);
-            this.handler.setBoolean(this.state.lastKey, false);
+            this.handler.setBoolean(this.state.lastKey as string, false);
             return true;
         }
         if (this.peekChar() == TRUE_STR.charCodeAt(0)) {
             this.readAndAssert(TRUE_STR);
-            this.handler.setBoolean(this.state.lastKey, true);
+            this.handler.setBoolean(this.state.lastKey as string, true);
             return true;
         }
 
@@ -325,7 +320,7 @@ export class JSONDecoder<JSONHandlerT extends JSONHandler> {
     private parseNull(): bool {
         if (this.peekChar() == NULL_STR.charCodeAt(0)) {
             this.readAndAssert(NULL_STR);
-            this.handler.setNull(this.state.lastKey);
+            this.handler.setNull(this.state.lastKey as string);
             return true;
         }
         return false;
diff --git a/package-lock.json b/package-lock.json
index 0593090..8e5e857 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4,6 +4,36 @@
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
+    "@as-pect/assembly": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/@as-pect/assembly/-/assembly-2.3.1.tgz",
+      "integrity": "sha512-KYBhyTEnaVcJjN/1EpzLhpbUHKT3pJjCPxm+Mdc7obnZ9EdVz6vN/lw+BQjeL4cUi1YLsnvgl8ftXcup5jVbQA==",
+      "dev": true
+    },
+    "@as-pect/cli": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/@as-pect/cli/-/cli-2.3.1.tgz",
+      "integrity": "sha512-ipcxrXnK9Xj1Foy92nSRsganapB+yxFe4HJ/RuwnjRQ9s8bqu0UwH12XbiHktcK7bJMs1H77/sqbQVxqoYHQcA==",
+      "dev": true,
+      "requires": {
+        "@as-pect/assembly": "^2.3.1",
+        "@as-pect/core": "^2.3.1",
+        "chalk": "^2.4.2",
+        "glob": "^7.1.4"
+      }
+    },
+    "@as-pect/core": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/@as-pect/core/-/core-2.3.1.tgz",
+      "integrity": "sha512-iwd4MkGuO1wZqo9/sPlT567XYK0PkMLzBvwfkXOM2zq1wwuc5GZQrKoofgYorA40KI0edJW39djtOmPwIhx2vA==",
+      "dev": true,
+      "requires": {
+        "@as-pect/assembly": "^2.3.1",
+        "chalk": "^2.4.2",
+        "csv-stringify": "^5.3.0",
+        "long": "^4.0.0"
+      }
+    },
     "@protobufjs/utf8": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/@protobufjs/utf8/-/utf8-1.1.0.tgz",
@@ -22,21 +52,15 @@
     "as-pect": {
       "version": "github:jtenner/as-pect#38025ef6ff7bf5a1727bbf685f98147d11598a71",
       "from": "github:jtenner/as-pect",
-      "dev": true,
-      "requires": {
-        "chalk": "^2.4.2",
-        "csv-stringify": "^5.3.0",
-        "glob": "^7.1.4",
-        "long": "^4.0.0"
-      }
+      "dev": true
     },
     "assemblyscript": {
-      "version": "github:assemblyscript/assemblyscript#5a8eee0befabf7bdef20960bc5d0d4c5246e7603",
+      "version": "github:assemblyscript/assemblyscript#addb99eff250af2af0241442d45ff3d23434e6f1",
       "from": "github:assemblyscript/assemblyscript",
       "dev": true,
       "requires": {
         "@protobufjs/utf8": "^1.1.0",
-        "binaryen": "84.0.0-nightly.20190522",
+        "binaryen": "87.0.0-nightly.20190716",
         "glob": "^7.1.4",
         "long": "^4.0.0",
         "opencollective-postinstall": "^2.0.0",
@@ -200,7 +224,7 @@
     },
     "path-is-absolute": {
       "version": "1.0.1",
-      "resolved": "https://registry.npmjs.org/path-is-absolute/-/path-is-absolute-1.0.1.tgz",
+      "resolved": "http://registry.npmjs.org/path-is-absolute/-/path-is-absolute-1.0.1.tgz",
       "integrity": "sha1-F0uSaHNVNP+8es5r9TpanhtcX18=",
       "dev": true
     },
diff --git a/package.json b/package.json
index 2542ef4..b3f03a5 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,8 @@
   },
   "devDependencies": {
     "assemblyscript": "github:assemblyscript/assemblyscript",
-    "as-pect": "github:jtenner/as-pect"
+    "as-pect": "github:jtenner/as-pect",
+    "@as-pect/cli": "^2.2.0"
   },
   "dependencies": {}
 }