Unable to set global variable from function

Grafana k6 OSS Support
1

I am trying to create a function that increments a padded counter like “001”, but I can’t seem to set my global variable from within the function.

  // Initialize step number
  let step = "001";

  // Print vuser number and iteration count
  console.log(`VU: ` + vuser + ` ITER: ` + iter + ` STEP: ` + step + ` START`);

  res = http.get(`https://` + tenant, {
    tags: { name: step + ` - https://` + tenant },
  });
  checkStatus(res, vuser, iter, step, 302);
  stepInc(step);

function stepInc(step) {
  step = parseFloat(step);
  step++;
  step = step.toString();
  step = step.padStart(3, '0');
}

The function resolves all of the transformations of step correctly, but I can’t seem to write it back to the global variable step. Am I missing something here?

2

Ideally, I would call stepInc() from within checkStatus(), but I can’t even get this to work.

3

Hello!

In JavaScript, primitives (like numbers) are passed by value, while objects are passed by reference. In order to do what you’re wanting, you’d have to write something like this:

let step = {};
step.num = 0;

export default function() {
  console.log("step.num: " + step.num);
  incStep(step);
}

function incStep(step) {
  step.num++;
}

Not particularly intuitive if, like me, you’re coming from a C#/Java background…!

4

Hmm… now how would I call this from within another function? I have tried ${step.num}, but it wasn’t too happy about that.

function checkStatus(res, vuser, iter, step, code) {
  check(res, {
    "Status: OK": (res) => res.status === code,

  }) || fail(" - - - Checks failed: " + res.url + " - - - Expected: " + code + " - - - Received: " + res.status + ` (vuser: ` + vuser + `, iter: ` + iter + `) ` + res.body);

  // Print out the current step to the console
  console.log(`VU: ` + vuser + ` ITER: ` + iter + ` STEP: ` + `${step}` + `-` + res.url)

  stepInc( ??? );

  sleep(2);
}
5

We’ll need a more complete code sample to figure out what you’re trying to do (i.e. your step declaration, but ideally you’re whole script minus anything sensitive).

6

You have no idea how much I appreciate this help, btw.

So below is my hacky workaround. What I am trying to have have happen is:

  1. The checkStatus() function should call the stepInc() function.
  2. The stepInc() function should read the global variable step and read/set it directly.
    // Compare the HTTP code retuned with what is expected, and fail the step if it does not match
    function checkStatus(res, vuser, iter, step, code) {
      check(res, {
        "Status: OK": (res) => res.status === code,

      }) || fail(" - - - Checks failed: " + res.url + " - - - Expected: " + code + " - - - Received: " + res.status + ` (vuser: ` + vuser + `, iter: ` + iter + `) ` + res.body);

      // Print out the current step to the console
      console.log(`VU: ` + vuser + ` ITER: ` + iter + ` STEP: ` + `${step}` + `-` + res.url)

      sleep(2);
    }

    function stepInc(step) {
      step = parseFloat(step);
      step++;
      step = step.toString();
      step = step.padStart(3, '0');
    }

      // Initialize step number
     let step = 1;

      // Print vuser number and iteration count
      console.log(`VU: ` + vuser + ` ITER: ` + iter + ` STEP: ` + step + ` START`);

      res = http.get(`https://` + tenant, {
        tags: { name: `00` + step + ` - https://` + tenant },
      });
      checkStatus(res, vuser, iter, step, 302);
      step++;

      res = http.get(`https://` + tenant + `/Platform/`, {
        tags: { name: `00` + step + ` - https://` + tenant + `/Platform/` },
      });
      checkStatus(res, vuser, iter, step, 302);
      step++;
7

Hi @leathej1 ,

From the latest code that you’ve posted step doesn’t look to be global.

If it is global - defined on the same levels as export default function() ... as in :

import http from "k6/http";
let step = 0; // this is global variable
export default function() {
   // here you can do w/e with step and if you haven't define one in 
   // the scope of this function it will change the global one
   step++; // this touches the global
}

function touchLocalStep(step) { // here step is an argument and is *not* the global one
  step++ // touches the local argument, which is copied by value as argument so it won't be seen outside the function
}

so you can either have it be global or you can have it locally (or have it both, but it will be a different variable).

As far as I can see from your sample you can just step++ wherever you want and when you will be using it you can have a formatStep as in

function formatStep(arg) { // I specifically changed it to not be called `step` here
      return arg.toString().padStart(3, '0');
}

and now you can move the definition of step in the default function, so it is local for that function, do step++ where you need to increase it and whenever you need to have it as a string with leading 0 call fortmatStep(step) and use the result instead.

Hope this helps you

8

Oh, wow - how did I miss that it wasn’t at the same level as the default function…

You saved me again- thanks!