Issue with Contract function return value data type

Question

I am using a simple contract

Contract code

contract Bank {
    address public owner;
    mapping(address => uint) private customerBalance;
    event fallbackCalled(address, uint256);
    event deposit(address, uint256);

    constructor() public {
        owner = msg.sender;
    }

    /** Customer Deposit payable function */
    function depositFunds(uint _value) external payable returns(bool) {
        require(_value > 0, "values not greater then zero");
        customerBalance[msg.sender] += _value;
        emit deposit(msg.sender, _value);
        return true;
    }

    /** Fetch Customer Balance */
    function getCustomerBalance() public view returns(uint) {
        return customerBalance[msg.sender];
    }

    function () external payable {
        emit fallbackCalled(msg.sender, msg.value);
    }
}

Test case --->

describe('Customer should able to deposit funds', () => {
  it('customer balance should be positive ', async () => {
    // Deposite money into Bank from account[1]  #2
    let _value = 10;
    const result = await deployedInstance.methods.depositFunds(_value).send({
      from: accounts[1]
    });

    // Fetch the balance of account[1] and it should be equal to 1
    let accountBalance = await deployedInstance.methods.getCustomerBalance().call({
      from: accounts[1]
    });

    expect(accountBalance).toBe(_value);
  })
})

---

Test case Result

expect(received).toBe(expected) // Object.is equality

Expected: 10
Received: "10"

**Difference:** Comparing two different types of values. Expected number but received string.

---

When I'm performing my unit testing that time, test case is failing caz customer balance value is coming as String from Contract call but I am supplying a number value from Testcase..

I have also check the offical documentation which also shows an exmple where they are fetching uint but getting string.

https://web3js.readthedocs.io/en/1.0/web3-eth-contract.html?#id18

Is there any specific reasons for returning strings.

Regards Dev

Answer 1

You will always get a string that contains a BigNumber because JavaScript itself has no equivalent type for an int or uint with 256 bits of precision.

They often contain interesting syntax ([]). Use toString(10) and keep in mind that loss of precision will happen. That could effect tests, but shouldn't if you use smallish numbers.

Have a look at this: https://github.com/ethereum/wiki/wiki/JavaScript-API#a-note-on-big-numbers-in-web3js

BigNumber has math methods, e.g. myNumber.add(1) so you can perform math without loss of precision. So, generally, reserve the conversion to human-readable format for UI concerns.

Hope it helps.