Ethereum: TypeError: X is not a function (Uncaught (in promise) error)
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Ethereum Error: TypeError: X is not a function
As a developer working with Ethereum smart contracts, you are probably no stranger to the complex world of programming languages and libraries. However, when using certain Ethereum contract methods, you may encounter an error that seems nonsensical at first glance. In this article, we will find out what causes this issue and provide a solution.
Problem: TypeError: X is not a function
When you try to call a method in your Ethereum contract using contract.methods.methodName(), it throws an error stating that “X” is not a function. This may seem like a generic error message, but it is actually more specific.
Problem: Unbound Constructor
In most programming languages, including JavaScript and some other libraries, when you call a method on an object without specifying the object itself (i.e. “X”), it will look for a constructor function defined elsewhere. However, in this case, we are working on a contract, not a class.
Fix: Bind the constructor
To fix this issue, you need to bind the constructor of the contract method to an instance of the contract itself. This is done using the bind() method provided by the call function.
contract.methods.myMethod.bind(this).call();
In this example, we bind the constructor « my Method » to « this » (i.e. our contract instance), so we can call it without specifying « X ».
Best practices
To avoid similar issues in the future:
- Make sure your methods are defined as constructors (« constructor X() »), and not as regular functions.
- Use the bind() method when calling a method on a contract instance.
With these fixes and best practices, you should be able to resolve the TypeError: X is not a function error with your Ethereum smart contract.
Code example
Here is an example code snippet that shows how to fix this issue:
import * as ethers from 'ethers';
const MyContract = artifacts.require('MyContract');
contract('MyContract', async (accounts) => {
const instance = await MyContract.new();
const myMethod = instance.methods.myMethod;
// Call myMethod without specifying X
console.log(await myMethod()); // Output: error typeError: X is not a function
// Using bind() to specify this fixes the issue:
const result = await myMethod.bind(this).call();
console.log(result);
});
Remember to replace ‘MyContract’ with the actual name of the contract and change the code accordingly.