Blockchain By Example

Callbacks

Web3.js is designed to work with a local RPC node, and all of its functions use synchronous HTTP requests by default. If you want to make an asynchronous request, you can pass an optional callback as the last parameter to most functions. All callbacks us an error-first callback pattern, as follows:

web3.eth.foo(argument1,..,argumentn, function(error, result) {    if (!error) {        console.log(result);    }});