Reading table rows with EOSJS

Question

Is there a way to receive the return output of an action with EOSJS? Say for example I have an action that reads columns from a table, sums a row and returns the result. How would I structure the function in C++ so that it returns the result, and how would I process the result in an EOSJS call?

Answer 1

You have several ways to retrieve data from eos chain as i know. They differs a lot, so you should find a better one for you case.

#1. Get from table
As you noted there is getTableRows method in eosjs lib, and by default it returns packed response. You can pass option json: true to instruct library to unpack response for you.

eos.getTableRows({
    code:'CONTRACT_NAME',
    scope:'SCOPE_ACCOUNT (Normally contract)',
    table:'TABLE_NAME',
    json: true,
}).then(function(res) {
    console.log(res);
});

You can find other available options in json format definition

#2. Read execution logs
You can log some valuable info to "console" when your action is executed. Then to read those logs call getActions method from eosjs lib. It return a list of actions for specific account. See json definition for more info.

this.eos.getActions('CONTRACT_NAME').then(...)

Note #1: Make sure that node you query from is running with history_api_plugin and filter_on_accounts option in config file respect your CONTRACT_NAME.

Note #2: Api returns every action that somehow belongs to provided account. So you need to filter them to find interesting one (use transaction_id received when transaction submitted).

There also a possible ways using mongodb plugin, but i can't provide any more info on this.