Is there a way to inspect which variables (and lines of code) contribute to a value in Javascript? For example if I would inspect the parameter input in this code
let x=5;
let y=x+3;
function a(input) {
// analyzing input in this scope/context,
// i would like to see that it is a combination of
// x from line 1 and a constant '3' from line 2.
inspectDataFlow(input);
}
a(y);
I would like to get as output a data structure that would be something like this:
input (line 8)
y (line 2)
x (line 1)
"3" (line 2)
Purpose and goal
My goal for this would be to have a tool where you could see/change the value of a Javascript variable and it would automatically adjust the variables that the value originates from.
For example, you could have a function to draw shapes. And when you adjust visually the shapes that were drawn, the original variables for color, shape positions etc would update accordingly.
Something a bit like this but for editing arbitrary code, even after a user has modified the code lines:
http://yining1023.github.io/p5PlayGround/
Another idea I was thinking was to visualize how a variable has been composed: which lines it is a combination of and how they affect the result.
Potential approach
One approach for this I'm thinking about is to add instrumentation to the code with Esprima/Acorn that is then called on runtime. The instrumentation would keep track on which variables have been called on which lines (and scopes) and how they relate to each other, a bit like this:
http://alltom.com/pages/instrumenting-javascript/
I wonder if this would work and if there is a framework one could use for this? Or if one would have to do the instrumentation from scratch?
Related themes
This could be related to data flow analysis or use-define chains, but I'm not sure, since I don't know much about compilers.
https://en.wikipedia.org/wiki/Use-define_chain
My first idea was that this could be done using static analysis with something like Esprima/Acorn, but I'm not sure if that is the right way, or if this could be done with some custom Javascript interpreter instead.
