Mastering JavaScript Functional Programming - Second Edition

Solution 2 – using a global flag

The solution most people would probably think of first is using some global variable to record whether the user has already clicked on the button. You'd define a flag named something like clicked, initialized with false. When the user clicks on the button, if clicked was false, you'd change it to true and execute the function; otherwise, you wouldn't do anything at all. See all of this in the following code:

let clicked = false;...function billTheUser(some, sales, data) {  if (!clicked) {    clicked = true;    window.alert("Billing the user...");    // actually bill the user  }}

For more good reasons not to use global variables, read http://wiki.c2.com/?GlobalVariablesAreBad.

This obviously works, but it has several ...