Maintaining Context In Asynchronous JS: web3.eth.getBalance() as Example
I'm currently working with nodejs and web3, and running into problems with the asynchronous model, and perhaps the specific implementation of web3's calls. The code below will provide my specific problem, and I believe the answer will be a pattern that can be used elsewhere.
The core question: how do I get the balance using the getBalance request while retaining context of the account for which I queried?
Code simplified for brevity.
I have a list:
var ethAccounts = ['0xabc', '0xdef', '0x123'];
My code will iterate through the list, getting the balance of each and doing something with it. Simple, right? I can use getBalance(), prototyped as:
web3.eth.getBalance( account, blockNumber(optional), callback (optional) )
The catch: getBalance is an asynchronous call that returns a Promise.
var balance = web3.eth.getBalance( ethAccounts[0] );
.. balance won't be what I need when it returns.
The official guidance is:
web3.eth.getBalance("0x407d73d8a49eeb85d32cf465507dd71d507100c1")
.then(console.log);
> "1000000000000"
I don't need the value at the console, so I build a function to catch the value.
web3.eth.getBalance(ethAccounts[0]).then(
function( value ) {
var balance = value;
// In this scope, I *can't see* ethAccounts[0]
console.log(balance);
}
);
In my function block, I need both the account and the value.
Perhaps the callback can help:
function testCallback( value1, value2 ) {
console.log(value1 + ", " + value2 );
}
web3.eth.getBalance(ethAccounts[0], undefined, testCallback );
Console output will be:
100000000000000000000, undefined
I have tried a number of scenarios: adding parameters to the callback, to the handler function, trying to cheat the promise with "await". So far I don't have a single pattern through which I can retain context.
Am I missing a simple Javascript of asynchronous pattern? How can I receive the balance in the same scope as I have the account in the request?
Thanks much!
javascript node.js asynchronous ethereum web3
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
add a comment |
I'm currently working with nodejs and web3, and running into problems with the asynchronous model, and perhaps the specific implementation of web3's calls. The code below will provide my specific problem, and I believe the answer will be a pattern that can be used elsewhere.
The core question: how do I get the balance using the getBalance request while retaining context of the account for which I queried?
Code simplified for brevity.
I have a list:
var ethAccounts = ['0xabc', '0xdef', '0x123'];
My code will iterate through the list, getting the balance of each and doing something with it. Simple, right? I can use getBalance(), prototyped as:
web3.eth.getBalance( account, blockNumber(optional), callback (optional) )
The catch: getBalance is an asynchronous call that returns a Promise.
var balance = web3.eth.getBalance( ethAccounts[0] );
.. balance won't be what I need when it returns.
The official guidance is:
web3.eth.getBalance("0x407d73d8a49eeb85d32cf465507dd71d507100c1")
.then(console.log);
> "1000000000000"
I don't need the value at the console, so I build a function to catch the value.
web3.eth.getBalance(ethAccounts[0]).then(
function( value ) {
var balance = value;
// In this scope, I *can't see* ethAccounts[0]
console.log(balance);
}
);
In my function block, I need both the account and the value.
Perhaps the callback can help:
function testCallback( value1, value2 ) {
console.log(value1 + ", " + value2 );
}
web3.eth.getBalance(ethAccounts[0], undefined, testCallback );
Console output will be:
100000000000000000000, undefined
I have tried a number of scenarios: adding parameters to the callback, to the handler function, trying to cheat the promise with "await". So far I don't have a single pattern through which I can retain context.
Am I missing a simple Javascript of asynchronous pattern? How can I receive the balance in the same scope as I have the account in the request?
Thanks much!
javascript node.js asynchronous ethereum web3
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is ifethAccountsorethAccounts[0]gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.
– Felix Kling
Nov 20 '18 at 21:56
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01
add a comment |
I'm currently working with nodejs and web3, and running into problems with the asynchronous model, and perhaps the specific implementation of web3's calls. The code below will provide my specific problem, and I believe the answer will be a pattern that can be used elsewhere.
The core question: how do I get the balance using the getBalance request while retaining context of the account for which I queried?
Code simplified for brevity.
I have a list:
var ethAccounts = ['0xabc', '0xdef', '0x123'];
My code will iterate through the list, getting the balance of each and doing something with it. Simple, right? I can use getBalance(), prototyped as:
web3.eth.getBalance( account, blockNumber(optional), callback (optional) )
The catch: getBalance is an asynchronous call that returns a Promise.
var balance = web3.eth.getBalance( ethAccounts[0] );
.. balance won't be what I need when it returns.
The official guidance is:
web3.eth.getBalance("0x407d73d8a49eeb85d32cf465507dd71d507100c1")
.then(console.log);
> "1000000000000"
I don't need the value at the console, so I build a function to catch the value.
web3.eth.getBalance(ethAccounts[0]).then(
function( value ) {
var balance = value;
// In this scope, I *can't see* ethAccounts[0]
console.log(balance);
}
);
In my function block, I need both the account and the value.
Perhaps the callback can help:
function testCallback( value1, value2 ) {
console.log(value1 + ", " + value2 );
}
web3.eth.getBalance(ethAccounts[0], undefined, testCallback );
Console output will be:
100000000000000000000, undefined
I have tried a number of scenarios: adding parameters to the callback, to the handler function, trying to cheat the promise with "await". So far I don't have a single pattern through which I can retain context.
Am I missing a simple Javascript of asynchronous pattern? How can I receive the balance in the same scope as I have the account in the request?
Thanks much!
javascript node.js asynchronous ethereum web3
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
I'm currently working with nodejs and web3, and running into problems with the asynchronous model, and perhaps the specific implementation of web3's calls. The code below will provide my specific problem, and I believe the answer will be a pattern that can be used elsewhere.
The core question: how do I get the balance using the getBalance request while retaining context of the account for which I queried?
Code simplified for brevity.
I have a list:
var ethAccounts = ['0xabc', '0xdef', '0x123'];
My code will iterate through the list, getting the balance of each and doing something with it. Simple, right? I can use getBalance(), prototyped as:
web3.eth.getBalance( account, blockNumber(optional), callback (optional) )
The catch: getBalance is an asynchronous call that returns a Promise.
var balance = web3.eth.getBalance( ethAccounts[0] );
.. balance won't be what I need when it returns.
The official guidance is:
web3.eth.getBalance("0x407d73d8a49eeb85d32cf465507dd71d507100c1")
.then(console.log);
> "1000000000000"
I don't need the value at the console, so I build a function to catch the value.
web3.eth.getBalance(ethAccounts[0]).then(
function( value ) {
var balance = value;
// In this scope, I *can't see* ethAccounts[0]
console.log(balance);
}
);
In my function block, I need both the account and the value.
Perhaps the callback can help:
function testCallback( value1, value2 ) {
console.log(value1 + ", " + value2 );
}
web3.eth.getBalance(ethAccounts[0], undefined, testCallback );
Console output will be:
100000000000000000000, undefined
I have tried a number of scenarios: adding parameters to the callback, to the handler function, trying to cheat the promise with "await". So far I don't have a single pattern through which I can retain context.
Am I missing a simple Javascript of asynchronous pattern? How can I receive the balance in the same scope as I have the account in the request?
Thanks much!
javascript node.js asynchronous ethereum web3
javascript node.js asynchronous ethereum web3
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
asked Nov 20 '18 at 21:53
Colin JaccinoColin Jaccino
1
1
" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is ifethAccountsorethAccounts[0]gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.
– Felix Kling
Nov 20 '18 at 21:56
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01
add a comment |
" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is ifethAccountsorethAccounts[0]gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.
– Felix Kling
Nov 20 '18 at 21:56
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01
" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is if
ethAccounts or ethAccounts[0] gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.– Felix Kling
Nov 20 '18 at 21:56
" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is if
ethAccounts or ethAccounts[0] gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.– Felix Kling
Nov 20 '18 at 21:56
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01
add a comment |
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" // In this scope, I *can't see ethAccounts[0]"* Sure you can, at least in the example you provided. JavaScript has lexical scope. The only reason this wouldn't work is if
ethAccountsorethAccounts[0]gets modified before the callback is executed. Please provide a Minimal, Complete, and Verifiable example.– Felix Kling
Nov 20 '18 at 21:56
What was the problem with await?
– nikos fotiadis
Nov 21 '18 at 7:01