"uncaught TypeError: a.indexOf is not a function" error when opening new foundation project

javascript

prompt-engineering

linting

debugging

byAnton Shumikhin·Nov 6, 2024

The error a.indexOf is not a function rears its ugly head when a is either not a string or an array as indexOf is a function of these types:

let aArray = []; // If 'a' should be an array
aArray.indexOf('value'); // Yep, this works fine! 🚀

let aString = ''; // If 'a' should be a string
aString.indexOf('substring'); // Sure thing, this is fine too! 🌟

The a could have been accidentally reassigned to a non-indexable type, like say an object or function. That's like passing me a spoon when I asked for a fork!

But, when we're discussing Foundation projects, this issue could also potentially pop up from outdated jQuery syntax or a mix-up in script loading order. Always ensure that the jQuery file is correctly loaded first before Foundation's JavaScript is called.

Digging deeper: Essential checks and fixes

Place scripts in correct order and verify script version

Ah yes, the pecking order! Always load the compatible version of jQuery before any Foundation scripts. Don't let your scripts live in a chaotic world!

<!-- Ensuring peace in script tag land -->
<script src="path-to/jquery.js"></script> <!-- jQuery first! ☝️ -->
<script src="path-to/foundation.js"></script> <!-- Then Foundation! ✌️ -->

Replace those deprecated jQuery methods

The oldies need to go. Replace all deprecated event aliases like .click(), .keypress(), etc., with the newer and shiny .on() event handler. Out with the old, in with the new - that's the motto!

// Deprecated way
$(document).ready(function() {
  $('#element').click(function() {
    // The click function is as old as my grandma 🧓
  });
});

// The new way
$(document).ready(function() {
  $('#element').on('click', function() {
    // Welcome to the future, young padawan! 🚀
  });
});

Initialize Foundation like a boss

Are you telling Foundation what to do? Ensure the initialization $(document).foundation(); command is present in your app.js:

$(document).foundation(); // Maybe now Foundation will listen to you 😂

Get assistance from jQuery migrate

When switching bases, always seek help. Use the jQuery Migration Plugin to breeze through old and new jQuery transitions:

<!-- Loaded after jQuery -->
<script src="path-to/jquery-migrate.min.js"></script> // Your convention buddy!

Avoid clash of the jQuery versions

Don't let jQuery versions wage a war! Stay clear of multiple jQuery versions and keep an eye for duplicate script tags. Remember, it's 'United We Stand'!

When all else fails, switch versions

When all hell breaks loose, switch to a compatible jQuery version:

<!-- A possible better companion for your project -->
<script src="path-to/jquery-2.1.0.min.js"></script> // The 'last resort' guy 😎

Becoming the JavaScript Sherlock: Debug and Preventive measures

Dig deep with Chrome DevTools

Use Chrome DevTools to pry open your JS variables, behave like a detective and make sure they have the expected values!

Foresee issues and act

Make it a habit to check variable types before performing operations. Be the Nostradamus of debugging!

Quality assurance with Linting

Let ESLint be your friend in creating a quality codebase. The linting tool will help you iron out any wrinkles in your code before they give you sleepless nights!