Learning JS: alert(...) and console.log(...)

The alert(message) method opens a pop-up dialog with message displayed and waits for the user to dismiss the pop-up window.

The following script:

let temp = 32.6;
let beanCounter = 4;
let reallyCool = true;
let motto = "I Rule";
temp = (temp - 32) * 5 / 9;
motto += " and so do you!";
let pos = Math.random();
// Now let's see what we've got
alert("temp is: " + temp);
alert("motto is: " + motto);
alert("And pos is: " + pos);

Will pop-up three (really annoying) messages, one after the other. To avoid the annoyance, the alert lines have been commented out in the source.

The console.log() is a much better tool to debug your code.

Instead of the alert() calls, you can just:

console.log("temp is: " + temp + " and motto is: " + motto);
console.log("And pos is: " + pos);

Normal visitors to your site will be none the wiser, since they won't see a thing, but you, with your developer tools console loaded, will be able to see what is going on with your JavaScript.