How to break on property change?

Question

The same question exists for javascript but I don't think the solutions listed there apply for typescript.

Firstly I've an object of type express.Request and I want to debug its body member:

function test(req : express.Request, res :express.Response, next:(err:any)=>void) {


  req.defineProperty(body, 'someProp', { //Property 'defineProperty' does not exist on type 'Request'.
    get: function () {
        return req._body;
    },

    set: function (value) {
        debugger; // sets breakpoint
        obj._someProp = value;
    }
});

Typescript compiles to javascript, so you debug it just the same way. Unless you use ts-node or something — Nurbol Alpysbayev, Oct 15 '18 at 15:08
@NurbolAlpysbayev But it won't let me compile the code/ I have a requirement to write only in typescript if possible. — AnArrayOfFunctions, Oct 15 '18 at 15:09
If the code doesn't compile, where are you planning to "break" the code? — JJJ, Oct 15 '18 at 15:11
@JJJ It won't let my apply `defineProperty` to my object but this is part of the debugging. — AnArrayOfFunctions, Oct 15 '18 at 15:23
Here's my suggestion: as this is an [XY problem](http://xyproblem.info), you would more likely get actual answers to your real problem if you showed the original code that doesn't work and asked directly why it doesn't work, instead of asking about the debugging method you've chosen which also doesn't work. — JJJ, Oct 15 '18 at 15:32
@JJJ Well you asked for it - https://stackoverflow.com/questions/52784174/how-to-diagnose-passport-authenticate/52806132#52806132 — AnArrayOfFunctions, Oct 15 '18 at 15:36

score 1 · Answer 1 · answered Oct 16 '18 at 01:43

The method you are looking for is called Object.defineProperty and it takes the object on which to define the property as the first argument. The proper usage would be something like this:

function test(req: express.Request, res: express.Response, next: (err: any) => void) {

    Object.defineProperty(req, 'body', {
        get: function () {
            return req._body;
        },

        set: function (value) {
            debugger; // sets breakpoint
            req._body = value;
        }
    });
}

How to break on property change?

1 Answers1