How to render value in promises on button click in react?

Question

I have two modules

App.jsx

import React from 'react';
import ReactDOM from 'react-dom';
import {accounts} from './contract.jsx';


class App extends React.Component{
    constructor(props){
    super(props);
    this.state={'text':'','accounts':'','clicked':false};
}
componentDidMount = () => {
    this.setState({'accounts':accounts()});
}
buttonAction = (e) => {
    this.setState({'clicked':true});
}
render(){
    return(
    <div align="center">
    <Button name="get all Accounts" action={this.buttonAction}/>
    {this.state.clicked ? <div>{this.state.accounts}</div> : null}
    </div>
    )}
}


const Button = (props) =>
    (<button onClick={props.action}>{props.name}</button>);

ReactDOM.render(<App/>,document.getElementById('root'));

and contract.jsx

import Web3 from 'web3';
var web3 = new Web3(Web3.givenProvider || 'http://localhost:8545');

let accounts = () => {
    // this is a promise
    web3.eth.getAccounts().then(function(result){console.log(result);})
    .catch(function(error){console.log(error.message)})
}
export {accounts};

I'm exporting accounts(a promise) function from contract.jsx to app.jsx. Since I can't return value from a promise, I need to assign the value to the state of App component inside the promise (check componentDidMount ). For that, I need to replace 'console.log(result)' in accounts function to 'this.setState({'accounts':result})'. But the component and accounts are in different modules and supposed to be independent. I cannot set the state of the App component inside my accounts function.

How can I assign the value from the promise to my state inside App component? Is there any other better way to do it? I could also use some code corrections to make my component work better.

Andrew Allison · Answer 1 · 2018-02-21T18:33:13.703

1

This is a little hacky, but you could try changing your constructor and render functions to:

constructor(props) {
  super(props);
  this.state = {
    'text': '',
    'accounts': null,
    'clicked': false
  };
}

...

render() {
  return(
    <div>
      { this.state['accounts'] ? (
          <div align="center">
            <Button name="get all Accounts" action={this.buttonAction}/>
            {this.state.clicked ? <div>{this.state.accounts}</div>:null}
          </div>
        ) : null 
      }
    </div>
  )
}

When the componentDidMount function does fire it should trigger a re-render. To store the value returned by the promise simply do the following in contract.jsx:

let accounts = () => {
  return web3.eth.getAccounts()
    .then( function(result) {
      return result; // Or it could be result.data, it depends
    }).catch( function(error) {
      console.error(error.message)
    });
}

edited Feb 21 '18 at 18:33

answered Feb 21 '18 at 17:07

Andrew Allison

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Yeah. But how do I store the promised value in my component state? – Uchiha Madara Feb 21 '18 at 17:19
The `accounts` function isn't working. From the little I know, I think we can't return a value from a promise. The only way is to set the promise result to a variable from inside the promise which I can't do because I want the promise to be independent of the component's any functionality. Please check this question once. [link](https://stackoverflow.com/questions/33242378/rendering-react-components-with-promises-inside-the-render-method) – Uchiha Madara Feb 21 '18 at 18:22

How to render value in promises on button click in react?

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