Mastering JavaScript Functional Programming

Solution #2 - use 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 change it to true, and execute the function; otherwise, you don't do anything at all:

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 problems that must be addressed:

• You are using ...