Add ERC20 decimal field support

src/__tests__/erc20/erc20.test.ts

@@ -213,7 +213,7 @@ test('erc20: transferFrom transaction', async () => {
   expect(tx.decoded).toEqual(decoded);
 });
 
-test('erc20: fetch symbol and totalSupply', async () => {
+test('erc20: fetch symbol, totalSupply and decimals', async () => {
   const query = `
     {
       block(number: 5600000) {
@@ -226,6 +226,7 @@ test('erc20: fetch symbol and totalSupply', async () => {
               tokenContract {
                 symbol
                 totalSupply
+                decimals
               }
               from {
                 account {
@@ -254,6 +255,7 @@ test('erc20: fetch symbol and totalSupply', async () => {
     tokenContract: {
       symbol: 'NULS',
       totalSupply: 4e25,
+      decimals: 18,
     },
     from: {
       account: {
@@ -285,6 +287,7 @@ test('erc20: fetch null symbol', async () => {
               tokenContract {
                 symbol
                 totalSupply
+                decimals
               }
               from {
                 account {
@@ -313,6 +316,7 @@ test('erc20: fetch null symbol', async () => {
     tokenContract: {
       symbol: null,
       totalSupply: 1e27,
+      decimals: 18,
     },
     from: {
       account: {
@@ -347,6 +351,7 @@ test('erc20: fetch token balance of recipient (account 0x0)', async () => {
                 }
                 symbol
                 totalSupply
+                decimals
               }
               from {
                 account {

src/abi/erc20.json

@@ -15,6 +15,14 @@
     "payable": false,
     "type": "function"
   },
+  {
+    "constant": true,
+    "inputs": [],
+    "name": "decimals",
+    "outputs": [{ "name": "", "type": "uint8" }],
+    "payable": false,
+    "type": "function"
+  },
   {
     "constant": true,
     "inputs": [],

src/erc20/model/index.ts

@@ -65,6 +65,13 @@ export class Erc20TokenContract {
       .call()
       .catch(() => undefined);
   }
+
+  public async decimals() {
+    return this._contract.methods
+      .decimals()
+      .call()
+      .catch(() => undefined);
+  }
 }
 
 export class Erc20TokenHolder {

src/erc20/schema/token.ts

@@ -8,5 +8,6 @@ type TokenContract {
   account: Account
   symbol: String
   totalSupply: Long
+  decimals: Int
 }
 `;