ECMAScript 6 Chaining Promises
I'm trying to chain promises, but the second one doesn't call the resolve function. What do I do wrong?
function getCustomers(){
let promise = new Promise(
function (resolve, reject){
console.log("Getting customers");
// Emulate an async server call here
setTimeout(function(){
var success = true;
if (success){
resolve( "John Smith"); // got the customer
}else{
reject("Can't get customers");
}
},1000);
}
);
return promise;
}
function getOrders(customer){
let promise = new Promise(
function (resolve, reject){
console.log("Getting orders");
// Emulate an async server call here
setTimeout(function(){
var success = true;
if (success){
resolve( "Order 123"); // got the order
}else{
reject("Can't get orders");
}
},1000);
}
);
return promise;
}
getCustomers()
.then((cust) => getOrders(cust))
.catch((err) => console.log(err));
console.log("Chained getCustomers and getOrders. Waiting for results");
The code prints "Getting orders" from the second function, but doesn't print "Order 123":
Getting customers Chained getCustomers and getOrders. Waiting for results Getting orders
Update. I wanted to insert the print on the console between chained methods that return promises. I guess something like this is not possible:
getCustomers() .then((cust) => console.log(cust)) //Can't print between chained promises? .then((cust) => getOrders(cust)) .then((order) => console.log(order)) .catch((err) => console.error(err));
You want to chain a success handler (for your resolve result "Order 123" ), not an error handler. So use then instead of catch :-)
getCustomers()
.then(getOrders)
.then((orders) => console.log(orders))
.catch((err) => console.error(err));
None of the promises was rejected, so the console.log(err) in your code was never called.
I wanted to insert the print on the console between chained methods that return promises. I guess something like this is not possible:
getCustomers()
.then((cust) => console.log(cust)) //Can't print between chained promises?
.then((cust) => getOrders(cust))
Yes it is possible, but you are intercepting a chain here. So the second then callback actually is not called with cust , but with the result of the first then callback - and console.log returns undefined , with which getOrders will get some problems.
You'd either do
var customers = getCustomers();
customers.then(console.log);
customers.then(getOrders).then((orders) => …)
or simpler just
getCustomers()
.then((cust) => { console.log(cust); return cust; })
.then(getOrders)
.then((orders) => …)
Here is a code example for Sequential execution for node.js using ES6 ECMAScript. Maybe somebody finds it useful. http://es6-features.org/#PromiseUsage https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise
var soapClient = easysoap.createClient(params);
//Sequential execution for node.js using ES6 ECMAScript
console.log('getAllFunctions:');
soapClient.getAllFunctions()
.then((functionArray) => {
return new Promise((resolve, reject) => {
console.log(functionArray);
console.log('getMethodParamsByName:');
resolve();
});
})
.then(() => {
return soapClient.getMethodParamsByName('test1'); //will return promise
})
.then((methodParams) => {
console.log(methodParams.request); //Console log can be outside Promise like here too
console.log(methodParams.response);
console.log('call');
return soapClient.call({ //Return promise
method: 'test1',
params: {
myArg1: 'aa',
myArg2: 'bb'
}
});
})
.then((callResponse) => {
console.log(callResponse); // response data as json
console.log('end');
})
.catch((err) => {
throw new Error(err);
});
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