javascript - Customized Stack Traces in Google Chrome Developer Tools?

I'm looking to customize the items that show up in the strack trace panel in the Scripts tab of Google Chrome's developers tools. Specifically, I want to filter out items in the stack trace and to add more descriptive names to some of the items on the stack trace without having to rename my objects and functions.

I found V8's Stack Trace API at but overriding Error.prepareStackTrace doesn't seem to have any effect.

I found V8's Stack Trace API at http://code.google./p/v8/wiki/JavaScriptStackTraceApi but overriding Error.prepareStackTrace doesn't seem to have any effect.

Share Improve this question asked May 28, 2011 at 19:05 soso 1811 silver badge8 bronze badges

how do you override it and where? Do you restart chrome after? How do you test your changes? Did you have any luck in other areas of chrome customizing? – gaRex Commented May 28, 2011 at 19:13

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3 Answers 3

Sorted by: Reset to default 7

The description on that page is definitely a little hard to follow, here's how it's done:

Error.prepareStackTrace = function(error, stack) {
    return stack;
};

var someObj = {
    someMethod : function () { 
        crash();
    }
}
function bar(barArg) { someObj.someMethod(); };
function foo(fooArg) { bar("barArgString"); };

function getTrace(e) {
    var stack = e.stack;
    var trace = "";

    for (var i = 0; i < stack.length; i++) {
        var frame = stack[i],
            func = frame.getFunction();

        trace += "\r" + frame.getThis() + "." + frame.getFunctionName();
    }
    return trace;
}

try {
    foo("fooArgString");
} catch (e) {
    alert("trace from catch(): " + getTrace(e));
}

This will show:

trace from catch(): 
[object Object].someObj.someMethod
[object Window].bar
[object Window].foo
[object Window].

The last frame is global scope (no function name).

Essentially your override of prepareStackTrace() causes error.stack to bee whatever you return from prepareStackTrace(). The trick is that the second argument to prepareStackTrace() is an Array of CallSite objects - the objects that support getThis(), getFunctionName() etc.

The code above overrides prepareStackTrace() so that it returns the Array of CallSite objects ("stack" parameter above), so this means when you try..catch an Error, Error.stack is going to contain the Array of CallSite objects instead of the usual stack trace in String form. Another approach would be to process the CallSite objects inside of your replacement prepareStackTrace() function and return your alternative stack trace as a String.

Note the CallSite objects are really finicky. Try to do frame.toString(), or just try to alert(frame) (implicitly this involves toString()) and it crashes and Chrome's developer tools show no error.

Here's the code that did the trick for me:

<head>
<script>
Error.prepareStackTrace = function()
{
        return "MyStackObject";
}
try {
  throw new Error();
} catch (e) {
  console.log(e.stack);
}
</script>
</head>

The documentation has moved here: https://github./v8/v8/wiki/Stack-Trace-API

Just put this at the beginning of your javascript code, it formats a nice stack trace:

Error.prepareStackTrace = function(error, stack) {
    var trace = '';
    var max_width = 0;
    for (var i = 0; i < stack.length; i++){
        var frame = stack[i];

        var typeLength = 0;
        typeLength = (frame.getTypeName() !== null && frame.getTypeName() !== '[object global]') ? frame.getTypeName().length : 0;
        typeLength = typeLength.length > 50 ? 50 : typeLength;

        functionlength = frame.getFunctionName() !== null ? frame.getFunctionName().length : '<anonymous>'.length;
        functionlength = functionlength > 50 ? 50 : functionlength;

        if (typeLength + functionlength > max_width)
            max_width = typeLength + functionlength;
    }

    for (var i = 0; i < stack.length; i++) {
        var frame = stack[i];

        var filepath = frame.getFileName();

        var typeName = '';  
        if (frame.getTypeName() !== null && frame.getTypeName() !== '[object global]')
            typeName = frame.getTypeName().substring(0, 50) + '.';

        var functionName = '<anonymous>';
        if (frame.getFunctionName() !== null)
            functionName = frame.getFunctionName().substring(0, 50);

        var space = '';
        var width = max_width - (typeName.length + functionName.length) + 2;
        space = Array(width).join(' ');
        var line = '  at ' + typeName + functionName + space + filepath + 
            ' (' + frame.getLineNumber() + 
            ':' + frame.getColumnNumber() + ')\n';

        trace += line;
    }
    return trace;
};

Here's an example to the test the code:

function A() { B(); }
function B() { C(); }
function C() { throw new Error('asd'); }
try {
    A();
} catch (e) { print(e + '\n' + e.stack); }

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