Can I put a data breakpoint which triggers if any variable is assigned to a string containing a certain substring?
For example, I want to reverse-engineer how a URL containing &ctoken= is constructed. It's done with complicated JavaScript where the goal is to obfuscate it.
If I could tell the JS VM to monitor all string variables and break when a certain substring appears on any variable, this would help me a lot.
Is this possible?
2 Answers
Answers 1
Before I start - as of my knowledge this is not possible.
What you'd need (even before creating the debugging feature) is String the built-in native object - which is supplied by the ECMAScript implementation to your scope - but already proxied.
Some explanation:
http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf
Standard built‑in objects are defined in this specification. An ECMAScript implementation may specify and supply additional kinds of built‑in objects. A built‑in constructor is a built‑ in object that is also a constructor.
String is, therefore, an already created instance without a proxy - doing this
const newString = 'newStringValue' will only add an object to the String Constant Pool and not notify a custom implemented subscriber.
more about the String Constant Pool: What is the difference between "text" and new String("text")?
Already implemented and exposed - for the built-in object String - would have to be something like (here in JS to make it understandable):
var proxiedString = new Proxy(String, { defineProperty(target, propKey, propDesc) { console.log('defined a new prop') }, }); proxiedString.x = 'newPropValue' the current built-in object String therefore would have to be the proxy already to which we could subscribe.
Answers 2
- You can use condition breakpoints at browser devTools, by right click with a menu.
- If you can write a js somewhere in a page, you can do this:
.
if(window.location.pathname.indexOf("&ctoken=") > -1){ debugger;// browser will put breakpoint automaticaly here, if condition is trully. console.dir(window.location); } 
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