Implement ERC20Wrapper and it's first method getBalanceAsync

1 files changed, 28 insertions, 0 deletions

diff --git a/src/contract_wrappers/erc20_wrapper.ts b/src/contract_wrappers/erc20_wrapper.ts
new file mode 100644
index 000000000..60b1887db
--- /dev/null
+++ b/src/contract_wrappers/erc20_wrapper.ts
@@ -0,0 +1,28 @@
+import * as _ from 'lodash';
+import * as BigNumber from 'bignumber.js';
+import {Web3Wrapper} from '../web3_wrapper';
+import {assert} from '../utils/assert';
+import {ContractWrapper} from './contract_wrapper';
+import * as TokenArtifacts from '../artifacts/Token.json';
+import {ERC20Contract} from '../types';
+
+export class ERC20Wrapper extends ContractWrapper {
+    constructor(web3Wrapper: Web3Wrapper) {
+        super(web3Wrapper);
+    }
+    /**
+     * Returns an owner's ERC20 token balance
+     */
+    public async getBalanceAsync(tokenAddress: string, ownerAddress: string): Promise<BigNumber.BigNumber> {
+        assert.isETHAddressHex('ownerAddress', ownerAddress);
+        assert.isETHAddressHex('tokenAddress', tokenAddress);
+
+        const contractInstance = await this.instantiateContractIfExistsAsync((TokenArtifacts as any), tokenAddress);
+        const tokenContract = contractInstance as ERC20Contract;
+        let balance = await tokenContract.balanceOf.call(ownerAddress);
+        // The BigNumber instance returned by Web3 is of a much older version then our own, we therefore
+        // should always re-instantiate the returned BigNumber after retrieval.
+        balance = _.isUndefined(balance) ? new BigNumber(0) : new BigNumber(balance);
+        return balance;
+    }
+}