Testing with Mocha, ReferenceError: alert is not defined

I am trying to do a test where this calculator app will return a false and show an alert message when invalid entries are given. However, I keep getting this error message:

  1 failing

  1) checkNum function
       Test 3: should return false for a string with invalid entries:
     ReferenceError: alert is not defined
      at checkNum (test\test.js:78:5)
      at Context.<anonymous> (test\test.js:58:24)
      at process.processImmediate (node:internal/timers:478:21)

The following is my code. How do I resolve this issue? Thank you.

var assert = require('assert');

describe('checkNum function',()=>{
    it('Test 3: should return false for a string with invalid entries', () => {
        const result = checkNum('abc$def');
        assert.equal(result, false);
    });
});

function checkNum(str) {
    for (var i = 0; i < str.length; i++) {
        var ch = str.charAt(i);
        if (ch < "0" || ch > "9") {
            if (ch != "/" && ch != "*" && ch != "+" && ch != "-" && ch != "."
                && ch != "(" && ch!= ")" && ch != "%") {
                alert("invalid entry!")
                return false
                }
            }
        }
        return true
}


  [1]: https://i.stack.imgur.com/MKiDi.png

>Solution :

This error occurred because Node.js was unable to execute alert,
the alert() is a method on the window object, which is only available in the browser

use console.log