Add assertions library and add them for all function args

package.json

@@ -31,6 +31,7 @@
     "node": ">=6.0.0"
   },
   "devDependencies": {
+    "@types/bignumber.js": "^4.0.2",
     "@types/chai": "^3.5.2",
     "@types/mocha": "^2.2.41",
     "@types/node": "^7.0.22",
@@ -46,9 +47,12 @@
     "tslint-config-0xproject": "^0.0.2",
     "typedoc": "^0.7.1",
     "typescript": "^2.3.3",
+    "web3-typescript-typings": "0.0.3",
     "webpack": "^2.6.0"
   },
   "dependencies": {
-    "ethereumjs-util": "^5.1.1"
+    "bignumber.js": "^4.0.2",
+    "ethereumjs-util": "^5.1.1",
+    "web3": "^0.19.0"
   }
 }

src/ts/0x.js.ts

@@ -1,4 +1,6 @@
+import * as BigNumber from 'bignumber.js';
 import * as ethUtil from 'ethereumjs-util';
+import {assert} from './utils/assert';
 
 /**
  * Elliptic Curve signature
@@ -15,6 +17,10 @@ export class ZeroEx {
      * by signing `data` with the private key corresponding to the `signer` address.
      */
     public static isValidSignature(data: string, signature: ECSignature, signer: ETHAddressHex): boolean {
+        assert.isString('data', data);
+        assert.isObject('signature', signature);
+        assert.isETHAddressHex('signer', signer);
+
         const dataBuff = ethUtil.toBuffer(data);
         const msgHashBuff = ethUtil.hashPersonalMessage(dataBuff);
         try {

src/ts/utils/assert.ts

@@ -0,0 +1,31 @@
+import * as _ from 'lodash';
+import * as BigNumber from 'bignumber.js';
+import Web3 = require('web3');
+
+export const assert = {
+    isBigNumber(variableName: string, value: BigNumber.BigNumber) {
+        const isBigNumber = _.isObject(value) && value.isBigNumber;
+        this.assert(isBigNumber, this.typeAssertionMessage(variableName, 'BigNumber', value));
+    },
+    isString(variableName: string, value: string) {
+        this.assert(_.isString(value), this.typeAssertionMessage(variableName, 'string', value));
+    },
+    isETHAddressHex(variableName: string, value: ETHAddressHex) {
+        const web3 = new Web3();
+        this.assert(web3.isAddress(value), this.typeAssertionMessage(variableName, 'ETHAddressHex', value));
+    },
+    isObject(variableName: string, value: object) {
+        this.assert(_.isObject(value), this.typeAssertionMessage(variableName, 'object', value));
+    },
+    isNumber(variableName: string, value: number) {
+        this.assert(_.isFinite(value), this.typeAssertionMessage(variableName, 'number', value));
+    },
+    assert(condition: boolean, message: string) {
+        if (!condition) {
+            throw new Error(message);
+        }
+    },
+    typeAssertionMessage(variableName: string, type: string, value: any) {
+        return `Expected ${variableName} to be of type ${type}, encountered: ${value}`;
+    },
+};

tsconfig.json

@@ -11,6 +11,7 @@
   },
   "include": [
     "./src/**/*",
-    "./test/**/*"
+    "./test/**/*",
+    "./node_modules/web3-typescript-typings/index.d.ts"
   ]
 }