return value after a promise

Question

I have a javascript function where I want to return the value that I get after the return method  Easier to see than explain  function getValue file       var val      lookupValue file  then function res          val   res val            return val      What is the best way to do this with a promise  As I understand it  the return val will return before the lookupValue has done it s then  but the I can t return res val as that is only returning from the inner function

User · Answer

The best way to do this would be to use the promise returning function as it is, like this

lookupValue(file).then(function(res) {
    // Write the code which depends on the `res.val`, here
});

The function which invokes an asynchronous function cannot wait till the async function returns a value. Because, it just invokes the async function and executes the rest of the code in it. So, when an async function returns a value, it will not be received by the same function which invoked it.

So, the general idea is to write the code which depends on the return value of an async function, in the async function itself.

User · Answer

Use a pattern along these lines   function getValue file      return lookupValue file      getValue  myFile txt   then function res         do whatever with res here        although this is a bit redundant  I m sure your actual code is more complicated

[javascript] return value after a promise

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