Introduction

Extension object from web3 will add rpc methods into current web3 module of the dapp.  There are many rpc calls that are not added as a method in web3 but they provide extension object with which we can add required rpc methods/calls into our working web3 module or instance.

Web3.extend

1. Parameters

• property  -  [ String ] (optional) : The name of the property to add to the module. If no property is set it will be added to the module directly.
• methods  -  It must be an array of method descriptions as follows :
  • name [ String ]  :  Name of the method to add.
  • call [ String ]  :  The RPC method name.
  • params [ Number ] (optional)  :  The number of parameters for that function. Default is always set to 0.
  • inputFormatter [ Array ] (optional)  :  Array of inputformatter functions. Each array item responds to a function parameter, so if you want some parameters not to be formatted, add a null instead.
  • outputFormatter [ Function ] (optional)  :  Used to format the output of the method.

2. Code Example

Let's add get balance and gas price super  RPC methods in our web3 module

const Web3 = require("web3");

Web3.extend({
    property: 'myModule',
    methods: [{
        name: 'getBalance',
        call: 'eth_getBalance',
        params: 2,
        inputFormatter: [web3.extend.formatters.inputAddressFormatter,
                          web3.extend.formatters.inputDefaultBlockNumberFormatter]
    },{
        name: 'getGasPriceSuperFunction',
        call: 'eth_gasPriceSuper',
        params: 2,
        inputFormatter: [null, web3.utils.numberToHex]
    }]
});