How to get the "stack trace" string?

[kiwenlau]

I'm trying to get the "stacktrace" string and return it other than log it in the console. However, following code doesn't work...

    function getStacktrace() {

        var stringifiedStack;
        var callback = function(stackframes) {
            stringifiedStack = stackframes.map(function(sf) {
                return sf.toString();
            }).join('\n');
            //console.log(stringifiedStack);
        };

        var errback = function(err) {
            console.log(err.message);
        };

        StackTrace.get().then(callback).catch(errback);

        //console.log(stringifiedStack);
        return stringifiedStack;
    }

[oliversalzburg]

What do you mean when you say it doesn't work?

Also, there's a mistake in your errback function; an extra ; in console.

[kiwenlau]

@oliversalzburg Thank you.
console.log(stringifiedStack) before return stringifiedStack just print undefined

[eriwen]

@kiwenlau The reason stringifiedStack is undefined when you return it is because StackTrace.get() runs asynchronously, so callback() has not been called yet.

You'll see that if you comment console.log(stringifiedStack); back in in both places, you'll see undefined and then the stacktrace.

[kiwenlau]

@eriwen Thank you!
Yes, it happens as you said.

undefined
a()@http://localhost:8080/test/test03.js:21:14
b()@http://localhost:8080/test/test03.js:25:5
c()@http://localhost:8080/test/test03.js:29:5
{anonymous}()@http://localhost:8080/test/test03.js:32:1

[kiwenlau]

The problems is how can I get the stacktrace string from callback()?

[eriwen]

Well, you have gotten the stacktrace and printed it to the console, already :)

Consider what you want to do with the stacktrace when you get it. Do you want to display it on the screen, or call a function with it? I'm afraid returning it won't be very useful, you'll need to call another function to do what you want.

Does that help?

[kiwenlau]

@eriwen I don't need to log it and I need to return it. And I don't know how to accomplish it...Thank you!

[eriwen]

I suggest you consider what you're doing with the stack after you've "returned" it. Note that it's not possible to be returned with the keyword. The asynchronous nature here dictates that you must provide a callback and that is the only way to "return" the stack trace.

callback does not have to be defined inline. It can be defined anywhere. You could pass the callback function to getStacktrace:

    function getStacktrace(callback) {
        var errback = function(err) {
            console.log(err.message);
        };

        StackTrace.get().then(callback).catch(errback);
    }


        var callback = function(stackframes) {
            var stack = stackframes.map(function(sf) {
                return sf.toString();
            }).join('\n');
            // Do something with stack here
        };

[kiwenlau]

@eriwen This is not I want. Thank you anyway! It seems to be impossible to return stacktrace string.

[bjentsch]

What about StackTrace.getSync...?

[niftylettuce]

I think what he is asking is to get a stringified stack trace into a format that is similar to err.stack. Calling stackframes.map(sf => sf.toString()).join('\n') does not yield the same format as new Error('foobar').stack.

[niftylettuce]

e.g. be able to pass stack frames to prepareStackTrace : https://github.com/nodejs/node/blob/6ce87c027dc2a16e1b8d85c753b52270ae0c6054/lib/internal/errors.js#L22-L44

[niftylettuce]

As of Node v12.3.1 you can simply call Error.prepareStackTrace(err, stackframes).

[niftylettuce]

The toString PR has been submitted stacktracejs/stackframe#23.