getField() doesn't work when using some library functions or iterator related functions/syntax/statements

[Soulike]

Hi, I'm developing a NodeProf analysis for logging all accesses to object/array fields. But I found getField() is not called when analyzing codes using some library functions (like Array.prototype.map()) or iterator related functions/syntax/statements (like Array.from(), spread expression, for...of statement). For example:

Analyzed Code

const array = [1, 2, 3, 4, 5];

function func()
{
    const arrayCopy = array.map(value => value);  // or [...array] or Array.from(array) or using for...of
}

func();

My Analysis Code

// DO NOT INSTRUMENT
(function (sandbox)
{
    function MyAnalysis()
    {
        this.getField = function (iid, base, offset, val, isComputed, isOpAssign, isMethodCall)
        {
            console.log(base);
            console.log(offset);
            console.log(val);
        };
    }

    sandbox.analysis = new MyAnalysis();
})(J$);

What I expect is that getField() should be called and telling me that offset: "0" "1" "2" "3" "4" of base: array are read with value 1 2 3 4 5 , respectively. Is it possible to achieve this?

[alexjordan]

Hi @Soulike,

NodeProf callbacks like getField work inside JavaScript code only. In your example the element access happens inside a builtin function, which cannot be instrumented and thus not analyzed. Working around this, you may want to try adding analysis models for certain builtin functions to your analysis, or as far as possible replace builtins with JS polyfills that can be analyzed.

[Soulike]

Hi @Soulike,

NodeProf callbacks like getField work inside JavaScript code only. In your example the element access happens inside a builtin function, which cannot be instrumented and thus not analyzed. Working around this, you may want to try adding analysis models for certain builtin functions to your analysis, or as far as possible replace builtins with JS polyfills that can be analyzed.

OK. Thank you for your reply. :)