Function Closures in For Loops Create Variable Reference Bugs

5/10 Medium

Functions defined inside for loops incorrectly capture the loop variable by reference rather than by value, causing all callback functions to reference the final loop value instead of their intended iteration value.

JavaScript
Category
dx
Workaround
partial
Stage
debug
Freshness
persistent
Scope
language
Recurring
Yes

Sources

Collection History

Query: “What are the most common pain points with C# for developers in 2025?”4/5/2026

Some developers may not consider the effects of using deferred execution methods in combination with captured variables... Apparently, the developers expected the delegate to execute prior to entering the loop.

Query: “What are the most common pain points with JavaScript for developers in 2025?”4/5/2026

Incorrect Use of Function Definitions Inside for Loops... Consider this code: var elements = document.getElementsByTagName('input'); var n = elements.length; for (var i = 0; i < n; i++) { elements[i].onclick = function() { console.log('This is element #' + i); };

Created: 4/5/2026Updated: 4/5/2026