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Leandro Severino
Leandro Severino
12,674 Points

when to use global variables?

I understand that declaring variables as locally as possible is good practice but what if we are caching DOM elements? Would it be better if I declare and define messageArea globally or would the pros of code organization outweigh the performance benefits? Just wanted to know your thoughts about it.

function showMessage(text){

let messageArea = document.getElementsByClassName('message')[0];
 messageArea.textContent = "";


1 Answer

Eric M
Eric M
11,545 Points

Well in this case you can always call getElementsByClassName again within whatever function needs it.

For a larger program the nodes getElementsByClassName stored in your global might not be valid later on if there are other functions changing the DOM heavily in between you storing it and retrieving it. And if you're calling it every time you need it then it might as well get called locally to the function that's actually using it.

There are times when it's fine to use a global variable. The short answer is "use them when they are only absolutely necessary" as you become more experienced you can go by "use them when they are the most elegant solution" but we can tend to consider them the best solution when they really aren't, which is why it's most often advised to avoid them.