Javascript: print function call

Question

I have a function like so:

const ILog = <T>(value: T): T => {
  console.log(value);
  return value;
}

It acts like console.log with the added benefit that it keeps the value it had.

However, I'd like to differenciate between calls of the same function:

let a = false;
let b = false;
let c = false;

ILog(a);
ILog(b);
ILog(c);

// current
$ node file.js
false
false
false

// expected
$ node file.js
ILog(a): false
ILog(b): false
ILog(c): false

Can some javascript black magic achieve this?

An example of how this would work would be like this:

const ILog = (name: string) => <T>(value: T): T => {
  console.log(`ILog(${name})`, value);
  return value;
}

ILog("[some_expression]")([some_expression]);

$ node file.js
ILog([some_expression]): [result]

Without repeating the expression in string form.

So you want the function to print the syntax it was called with? I'm not aware of any js tools to do that short of some silliness with `eval()`, but it wouldn't be called like `ILog(a)` anymore. — CollinD, Oct 12 '22 at 16:42
Would it be sufficient for you to use a [stack trace](https://stackoverflow.com/q/591857/1426891)? It's more verbose, but a call to `console.trace()` or a light processing of `new Error().stack` might give you the context you need to differentiate between calls. — Jeff Bowman, Oct 12 '22 at 17:42

score 0 · Answer 1 · answered Oct 12 '22 at 16:51

0

There's no magic way to do this, you could do something like this if you really wanted:

const ILog = <T>(value: T, argumentName: string): T => {
  console.log(`ILog(${argumentName}): ${value}`);
  return value;
}

const a = false;
ILog(a, "a");

Or using your existing ILog function,

ILog(`ILog(a): ${a}`);

answered Oct 12 '22 at 16:51

CollinD

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The first one is kinda what I've been doing, I posted this question cause I might learn smth new idk. – Carlo Augusto Bagnoli Gomez Oct 12 '22 at 17:02
The second one wouldn't really work tho, it doesn't keep the original value intact – Carlo Augusto Bagnoli Gomez Oct 12 '22 at 17:02
Like I said, there's no magic. Only the code at the original calling location can possibly be aware of the variable name. – CollinD Oct 12 '22 at 17:03
Also the main reason why I wanted to see a better way is bc some arguments can be convoluted like `ILog(!!a)` or `ILog(a.some(({ status }) => status === "smth")))` – Carlo Augusto Bagnoli Gomez Oct 12 '22 at 17:04
Regardless, `ILog` only gets a value. JS is pass-by-value, the `ILog` function sees no difference between `ILog(a.some(...))` and `ILog(false)`. The `ILog` function also does its own logging, which precludes another function from logging to the line before `ILog` does, so you literally cannot generate the output you want with a function that does its own call to `console.log` as every call to `console.log` creates a newline. – CollinD Oct 12 '22 at 17:06

Javascript: print function call

1 Answers1