The ABI of a contract provides various kinds of information about the contract other than implementation. The ABI generated by two different versions of compilers may not match as higher versions support more solidity features than lower versions; therefore, they will include extra things in the ABI. For example, the fallback function was introduced in the 0.4.0 version of Solidity so the ABI generated using compilers whose version is less than 0.4.0 will have no information about fallback functions, and these smart contracts behave like they have a fallback function with an empty body and a payable modifier. So, the API should be updated so that applications that depend on the ABI of newer solidity versions can have better information about the contract.

solcjs provides an API to update the ABI. Here is an example code to demonstrate this:

var abi = require("solc/abi"); 

var inputABI = [{"constant":false,"inputs":[],"name":"hello","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"}]; 
var outputABI = abi.update("0.3.6", inputABI) 

Here, 0.3.6 indicates that the ABI was generated using the 0.3.6 version of the compiler. As we are using solcjs version 0.4.8, the ABI will be updated to match the ABI generated by the 0.4.8 compiler version, not above it.

The output of the preceding code will be as follows:

[{"constant":false,"inputs":[],"name":"hello","outputs":[{"name":"","type":"string"}],"payable":true,"type":"function"},{"type":"fallback","payable":true}]