How do you find out the caller function in JavaScript?

Question

function main()
{
   Hello();
}

function Hello()
{
  // How do you find out the caller function is \'main\'?
}

Is there a way to find out the call

Answer 1

heystewart's answer and JiarongWu's answer both mentioned that the Error object has access to the stack.

Here's an example:

function main() {
  Hello();
}

function Hello() {
  var stack = new Error().stack;
  // N.B. stack === "Error\n  at Hello ...\n  at main ... \n...."
  var m = stack.match(/.*?Hello.*?\n(.*?)\n/);
  if (m) {
    var caller_name = m[1];
    console.log("Caller is:", caller_name)
  }
}

main();

Different browsers shows the stack in different string formats:

Safari  : Caller is: main@https://stacksnippets.net/js:14:8
Firefox : Caller is: main@https://stacksnippets.net/js:14:3
Chrome  : Caller is:     at main (https://stacksnippets.net/js:14:3)
IE Edge : Caller is:    at main (https://stacksnippets.net/js:14:3)
IE      : Caller is:    at main (https://stacksnippets.net/js:14:3)

Most browsers will set the stack with var stack = (new Error()).stack. In Internet Explorer the stack will be undefined - you have to throw a real exception to retrieve the stack.

Conclusion: It's possible to determine "main" is the caller to "Hello" using the stack in the Error object. In fact it will work in cases where the callee / caller approach doesn't work. It will also show you context, i.e. source file and line number. However effort is required to make the solution cross platform.

Answer 2

Why all of the solutions above look like a rocket science. Meanwhile, it should not be more complicated than this snippet. All credits to this guy

How do you find out the caller function in JavaScript?

var stackTrace = function() {

    var calls = [];
    var caller = arguments.callee.caller;

    for (var k = 0; k < 10; k++) {
        if (caller) {
            calls.push(caller);
            caller = caller.caller;
        }
    }

    return calls;
};

// when I call this inside specific method I see list of references to source method, obviously, I can add toString() to each call to see only function's content
// [function(), function(data), function(res), function(l), function(a, c), x(a, b, c, d), function(c, e)]

Answer 3

It's safer to use *arguments.callee.caller since arguments.caller is deprecated...

Answer 4

function Hello()
{
    alert("caller is " + Hello.caller);
}

Note that this feature is non-standard, from Function.caller:

Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

---

The following is the old answer from 2008, which is no longer supported in modern Javascript:

function Hello()
{
    alert("caller is " + arguments.callee.caller.toString());
}

Answer 5

Another way around this problem is to simply pass the name of the calling function as a parameter.

For example:

function reformatString(string, callerName) {

    if (callerName === "uid") {
        string = string.toUpperCase();
    }

    return string;
}

Now, you could call the function like this:

function uid(){
    var myString = "apples";

    reformatString(myString, function.name);
}

My example uses a hard coded check of the function name, but you could easily use a switch statement or some other logic to do what you want there.

Answer 6

Just console log your error stack. You can then know how are you being called

const hello = () => {
  console.log(new Error('I was called').stack)
}

const sello = () => {
  hello()
}

sello()