Uncaught Typeerror: Cannot Read Property 'magnificpopup' of Undefined

JavaScript Errors and How to Fix Them

JavaScript can be a nightmare to debug: Some errors it gives can exist very difficult to understand at kickoff, and the line numbers given aren't always helpful either. Wouldn't it be useful to accept a list where you could look to find out what they hateful and how to fix them? Here y'all go!

Below is a listing of the strange errors in JavaScript. Dissimilar browsers tin can give y'all different messages for the same fault, so there are several different examples where applicable.

How to read errors?

Before the list, let's rapidly look at the structure of an mistake message. Understanding the structure helps sympathise the errors, and you'll have less trouble if you run into any errors not listed here.

A typical error from Chrome looks similar this:

Uncaught TypeError: undefined is non a function

The construction of the mistake is equally follows:

1. Uncaught TypeError: This part of the message is normally non very useful. Uncaught means the error was not defenseless in a catch argument, and TypeError is the fault'southward proper noun.
2. undefined is non a role: This is the message part. With error messages, you have to read them very literally. For example in this case information technology literally means that the lawmaking attempted to apply undefined like information technology was a function.

Other webkit-based browsers, like Safari, requite errors in a similar format to Chrome. Errors from Firefox are similar, but do not always include the showtime role, and recent versions of Internet Explorer likewise give simpler errors than Chrome – merely in this case, simpler does not always mean ameliorate.

At present onto the actual errors.

Uncaught TypeError: undefined is not a office

Related errors: number is not a function, object is not a function, string is non a office, Unhandled Fault: 'foo' is not a function, Role Expected

Occurs when attempting to call a value like a part, where the value is not a function. For case:

var foo = undefined; foo();

This fault typically occurs if y'all are trying to telephone call a role in an object, but you typed the name wrong.

var ten = certificate.getElementByID('foo');

Since object properties that don't exist are undefined by default, the above would result in this fault.

The other variations such equally "number is not a function" occur when attempting to call a number like it was a function.

How to fix this error: Ensure the function name is correct. With this error, the line number will unremarkably point at the correct location.

Uncaught ReferenceError: Invalid left-mitt side in assignment

Related errors: Uncaught exception: ReferenceError: Cannot assign to 'functionCall()', Uncaught exception: ReferenceError: Cannot assign to 'this'

Caused by attempting to assign a value to something that cannot be assigned to.

The almost common instance of this error is with if-clauses:

if(doSomething() = 'somevalue')

In this example, the programmer accidentally used a unmarried equals instead of two. The message "left-manus side in assignment" is referring to the office on the left side of the equals sign, so like you can see in the above case, the left-paw side contains something you can't assign to, leading to the error.

How to fix this mistake: Brand sure you're not attempting to assign values to function results or to the this keyword.

Uncaught TypeError: Converting circular structure to JSON

Related errors: Uncaught exception: TypeError: JSON.stringify: Not an acyclic Object, TypeError: cyclic object value, Circular reference in value argument non supported

Always caused by a circular reference in an object, which is and so passed into JSON.stringify.

var a = { }; var b = { a: a }; a.b = b; JSON.stringify(a);

Because both a and b in the above example accept a reference to each other, the resulting object cannot be converted into JSON.

How to fix this error: Remove circular references similar in the example from whatsoever objects you lot want to convert into JSON.

Unexpected token ;

Related errors: Expected ), missing ) afterwards statement listing

The JavaScript interpreter expected something, just it wasn't there. Typically caused past mismatched parentheses or brackets.

The token in this fault tin can vary – it might say "Unexpected token ]" or "Expected {" etc.

How to fix this error: Sometimes the line number with this error doesn't point to the correct place, making it difficult to ready.

• An mistake with [ ] { } ( ) is normally caused by a mismatching pair. Check that all your parentheses and brackets accept a matching pair. In this case, line number will often betoken to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this will usually exist correct.
• Unexpected ; is unremarkably caused by having a ; inside an object or array literal, or within the argument list of a role call. The line number will commonly be correct for this example as well

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated Cord Literal, Invalid Line Terminator

A string literal is missing the closing quote.

How to fix this fault: Ensure all strings have the right endmost quote.

Uncaught TypeError: Cannot read property 'foo' of goose egg, Uncaught TypeError: Cannot read belongings 'foo' of undefined

Related errors: TypeError: someVal is null, Unable to get belongings 'foo' of undefined or null reference

Attempting to read null or undefined as if it was an object. For example:

var someVal = null; console.log(someVal.foo);

How to prepare this mistake: Ordinarily acquired by typos. Bank check that the variables used near the line number pointed past the mistake are correctly named.

Uncaught TypeError: Cannot ready property 'foo' of null, Uncaught TypeError: Cannot set property 'foo' of undefined

Related errors: TypeError: someVal is undefined, Unable to set up property 'foo' of undefined or null reference

Attempting to write zippo or undefined as if it was an object. For example:

var someVal = cypher; someVal.foo = one;

How to prepare this error: This too is ordinarily caused by typos. Check the variable names near the line the error points to.

Uncaught RangeError: Maximum call stack size exceeded

Related errors: Uncaught exception: RangeError: Maximum recursion depth exceeded, too much recursion, Stack overflow

Usually caused by a problems in program logic, causing infinite recursive function calls.

How to fix this error: Check recursive functions for bugs that could cause them to go along recursing forever.

Uncaught URIError: URI malformed

Related errors: URIError: malformed URI sequence

Acquired past an invalid decodeURIComponent call.

How to set up this error: Check that the decodeURIComponent call at the error's line number gets correct input.

XMLHttpRequest cannot load http://some/url/. No 'Admission-Control-Allow-Origin' header is present on the requested resources

Related errors: Cross-Origin Asking Blocked: The Same Origin Policy disallows reading the remote resource at http://some/url/

This error is always caused by the usage of XMLHttpRequest.

How to fix this error: Ensure the request URL is correct and information technology respects the same-origin policy. A skillful way to find the offending code is to look at the URL in the fault message and find it from your lawmaking.

InvalidStateError: An attempt was made to use an object that is not, or is no longer, usable

Related errors: InvalidStateError, DOMException lawmaking eleven

Means the code chosen a function that yous should not call at the current land. Occurs usually with XMLHttpRequest, when attempting to call functions on it before it'due south ready.

var xhr = new XMLHttpRequest(); xhr.setRequestHeader('Some-Header', 'val');

In this example, yous would get the error because the setRequestHeader function can only exist chosen later on calling xhr.open.

How to fix this error: Wait at the code on the line pointed by the error and make sure information technology runs at the correct fourth dimension, or add whatever necessary calls earlier it (such as xhr.open)

Conclusion

JavaScript has some of the nigh unhelpful errors I've seen, with the exception of the notorious Expected T_PAAMAYIM_NEKUDOTAYIM in PHP. With more familiarity the errors start to make more sense. Mod browsers also help, equally they no longer give the completely useless errors they used to.

What's the almost confusing error you've seen? Share the frustration in the comments!

Want to larn more nigh these errors and how to prevent them? Detect Problems in JavaScript Automatically with ESLint.

About Jani Hartikainen

Jani Hartikainen has spent over ten years building web applications. His clients include companies like Nokia and hot super secret startups. When not programming or playing games, Jani writes about JavaScript and loftier quality code on his site.

codeutopia.netjhartikainenPosts

johnsonspoself.blogspot.com

Source: https://davidwalsh.name/fix-javascript-errors

Share this post