Cannot find a function within the Promise

Question

Cannot find a function within the Promise

Here is the code snippet I am working with:

var c = function(address, abiJson){
    var _ = this;
    this.data = {
            wallet: false,
            account:{
                address: false
            },
            contract:{
                address: address
            }
    };
    this.abi = $.getJSON(abiJson, function(abi){
        _.data.abi = abi;
        if(typeof web3 !== 'undefined'){
            window.web3 = new Web3(web3.currentProvider);
            window.cont = web3.eth.contract(abi).at(address);
        }
    });
    this.getData = function(cb){
        if(typeof _.data.abi !== 'undefined'){
            _.updateData.done(() => {
                cb(_.data);
            });
        }
        else{
            _.abi.then(() => {_.updateData
            })
            .done(() => {
                cb(_.data);
            });
        }
    }
    this.updateData = Promise.all([
            _.get('x'),
            _.get('y')
        ])
        .then(values => { 
            _.data.x.y= values[0];
            _.data.x.z= values[1];
        })
        .then(() => {
            Promise.all([
                _.get('v', 1),
                _.get('v', 2),
            ])
            .then(values => {
                _.data.y = values;
            });
        });
    this.get = function(method, args){
        return new Promise(function(resolve, reject) {
            window.cont[method](args, function(error, result){
                if(!error) resolve(result);
            });
        });
    }
}

I have encountered an issue where when I call the function

_.get('x').then((x) => console.log (x))

outside the updateData function, all the data is retrieved successfully. However, when I utilize the getData function, errors are thrown for all the get functions stating that _.get is not a function.

I am struggling to identify where I may have made an error in my implementation. This is my first time working with JavaScript Promises.

javascript

Answer 1

Answer №1

Below is a condensed version of the question:

var C = function(address, abiJson){
    var _ = this;
    this.updateData = Promise.all([
            _.get('x'),
            _.get('y')
        ]);
    this.get = function( arg){ return Promise.resolve( arg)};
}
var c = new C();
c.updateData.then( values => console.log(values));

When calling get within the array initializer argument of the Promise.all call, an error occurs because get has not yet been added as a method of _ (which is assigned to this). The immediate problem can be resolved by adding the get method before creating the array:

var C = function(address, abiJson){
    var _ = this;
    // add get method first:
    this.get = function( arg){ return Promise.resolve( arg)};
    this.updateData = Promise.all([
            _.get('x'),
            _.get('y')
        ]);
}
var c = new C();
c.updateData.then( values => console.log(values));

Answer 2

Below is a condensed version of the question:

var C = function(address, abiJson){
    var _ = this;
    this.updateData = Promise.all([
            _.get('x'),
            _.get('y')
        ]);
    this.get = function( arg){ return Promise.resolve( arg)};
}
var c = new C();
c.updateData.then( values => console.log(values));

When calling get within the array initializer argument of the Promise.all call, an error occurs because get has not yet been added as a method of _ (which is assigned to this). The immediate problem can be resolved by adding the get method before creating the array:

var C = function(address, abiJson){
    var _ = this;
    // add get method first:
    this.get = function( arg){ return Promise.resolve( arg)};
    this.updateData = Promise.all([
            _.get('x'),
            _.get('y')
        ]);
}
var c = new C();
c.updateData.then( values => console.log(values));

Answer 3

Answer №2

_ variable is not valid in this context. It can be used as a function but not when creating an object. To maintain scope, you can use bind for regular functions. Arrow functions automatically retain the current scope. Here is an example code where _ has been replaced with 'this' and binded to the callback of getJSON. If arrow functions are used, bind is not necessary.

var c = function(address, abiJson){
    this.data = {
        wallet: false,
        account:{
            address: false
        },
        contract:{
            address: address
        }
    };
    this.abi = $.getJSON(abiJson, function(abi){
        this.data.abi = abi;
        if(typeof web3 !== 'undefined'){
            window.web3 = new Web3(web3.currentProvider);
            window.cont = web3.eth.contract(abi).at(address);
        }
    }.bind(this));
    
    this.getData = function(cb){
        if(typeof this.data.abi !== 'undefined'){
            this.updateData.done(() => {
                cb(this.data);
            });
        }
        else{
            this.abi.then(() => {this.updateData})
            .done(() => {
                cb(this.data);
            });
        }
    }
    
    this.get = function(method, args){
        return new Promise(function(resolve, reject) {
            window.cont[method](args, function(error, result){
                if(!error) resolve(result);
            });
        });
    }
    
    this.updateData = Promise.all([
        this.get('x'),
        this.get('y')
    ])
    .then(values => { 
        this.data.x.y= values[0];
        this.data.x.z= values[1];
    })
    .then(() => {
        Promise.all([
            this.get('v', 1),
            this.get('v', 2),
        ])
        .then(values => {
            this.data.y = values;
        });
    });

}

Answer 4

_ variable is not valid in this context. It can be used as a function but not when creating an object. To maintain scope, you can use bind for regular functions. Arrow functions automatically retain the current scope. Here is an example code where _ has been replaced with 'this' and binded to the callback of getJSON. If arrow functions are used, bind is not necessary.

var c = function(address, abiJson){
    this.data = {
        wallet: false,
        account:{
            address: false
        },
        contract:{
            address: address
        }
    };
    this.abi = $.getJSON(abiJson, function(abi){
        this.data.abi = abi;
        if(typeof web3 !== 'undefined'){
            window.web3 = new Web3(web3.currentProvider);
            window.cont = web3.eth.contract(abi).at(address);
        }
    }.bind(this));
    
    this.getData = function(cb){
        if(typeof this.data.abi !== 'undefined'){
            this.updateData.done(() => {
                cb(this.data);
            });
        }
        else{
            this.abi.then(() => {this.updateData})
            .done(() => {
                cb(this.data);
            });
        }
    }
    
    this.get = function(method, args){
        return new Promise(function(resolve, reject) {
            window.cont[method](args, function(error, result){
                if(!error) resolve(result);
            });
        });
    }
    
    this.updateData = Promise.all([
        this.get('x'),
        this.get('y')
    ])
    .then(values => { 
        this.data.x.y= values[0];
        this.data.x.z= values[1];
    })
    .then(() => {
        Promise.all([
            this.get('v', 1),
            this.get('v', 2),
        ])
        .then(values => {
            this.data.y = values;
        });
    });

}

Cannot find a function within the Promise

Answer №1

Answer №2

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