JavaScript — from callbacks to async/await
Diogo Spínola
4.4K14

If you chain multiple .then
You should always add a return at the end of their respective callbacks
Else they will execute at the same time

That is not true. Try the following code:

function foo () {
return new Promise(function(resolve, reject) {
setTimeout(resolve(“resolved value”), 1000);
});
};
foo().then(function (val) {
debugger;
console.log(first then");
}).then(function (val) {
debugger;
console.log("second then");
});

If you run this example you’ll see that “first then” is printed and only after that “second then” is printed in the console.

Note that, when a function doesn’t have an explicit return statement it returnsundefinedexplicitly. If return statement, from the then callback , is not a Promise it will be wrapped into a Promise explicitly.

Regarding this part:

“When a reject is caught if you have a .then chained to i
It will still execute that .then
You can see the .then as an “always executes”

I cannot understand what you’ve meant here.