Fullcalendar Uncaught Typeerror: Cannot Read Property 'striptime' of Undefined

JavaScript Errors and How to Gear up Them

JavaScript can exist a nightmare to debug: Some errors it gives tin be very difficult to understand at first, and the line numbers given aren't always helpful either. Wouldn't information technology be useful to have a list where you could expect to find out what they mean and how to fix them? Here you go!

Below is a list of the strange errors in JavaScript. Different browsers can give you different letters for the aforementioned mistake, and so there are several different examples where applicable.

How to read errors?

Before the listing, let'due south quickly look at the structure of an fault bulletin. Understanding the structure helps understand the errors, and you'll have less trouble if yous meet whatever errors not listed hither.

A typical fault from Chrome looks similar this:

Uncaught TypeError: undefined is non a function

The construction of the mistake is as follows:

1. Uncaught TypeError: This part of the bulletin is unremarkably non very useful. Uncaught means the error was not defenseless in a take hold of argument, and TypeError is the mistake's proper name.
2. undefined is not a function: This is the message part. With mistake messages, you lot take to read them very literally. For example in this case it literally means that the code attempted to employ undefined like it was a office.

Other webkit-based browsers, similar Safari, give errors in a like format to Chrome. Errors from Firefox are similar, simply do non always include the showtime office, and recent versions of Internet Explorer also give simpler errors than Chrome – but in this case, simpler does non always mean better.

Now onto the actual errors.

Uncaught TypeError: undefined is non a function

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

Occurs when attempting to call a value similar a role, where the value is not a function. For example:

var foo = undefined; foo();

This error typically occurs if you are trying to call a function in an object, simply you typed the proper name incorrect.

var x = document.getElementByID('foo');

Since object backdrop that don't exist are undefined past default, the above would result in this error.

The other variations such as "number is not a office" occur when attempting to call a number similar information technology was a function.

How to prepare this error: Ensure the role name is correct. With this error, the line number will ordinarily betoken at the correct location.

Uncaught ReferenceError: Invalid left-mitt side in consignment

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

Acquired past attempting to assign a value to something that cannot exist assigned to.

The virtually mutual example of this error is with if-clauses:

if(doSomething() = 'somevalue')

In this instance, the programmer accidentally used a single equals instead of two. The message "left-manus side in consignment" is referring to the part on the left side of the equals sign, so similar you can see in the above example, the left-hand side contains something y'all tin't assign to, leading to the error.

How to fix this error: Make 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 round reference in an object, which is then 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 take a reference to each other, the resulting object cannot exist converted into JSON.

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

Unexpected token ;

Related errors: Expected ), missing ) later on argument listing

The JavaScript interpreter expected something, merely information technology wasn't there. Typically caused past mismatched parentheses or brackets.

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

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

• An fault with [ ] { } ( ) is unremarkably caused past a mismatching pair. Bank check that all your parentheses and brackets take a matching pair. In this example, line number volition frequently point to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this will usually be right.
• Unexpected ; is ordinarily caused past having a ; within an object or array literal, or inside the argument list of a office phone call. The line number will usually be correct for this case every bit well

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated String Literal, Invalid Line Terminator

A string literal is missing the endmost quote.

How to gear up this mistake: Ensure all strings have the correct closing quote.

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

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

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

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

How to fix this error: Usually acquired by typos. Check that the variables used near the line number pointed by the error are correctly named.

Uncaught TypeError: Cannot set belongings 'foo' of zilch, Uncaught TypeError: Cannot set property 'foo' of undefined

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

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

var someVal = null; someVal.foo = one;

How to fix this mistake: This too is unremarkably caused by typos. Cheque the variable names near the line the mistake points to.

Uncaught RangeError: Maximum telephone call stack size exceeded

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

Usually caused by a bug in program logic, causing infinite recursive role calls.

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

Uncaught URIError: URI malformed

Related errors: URIError: malformed URI sequence

Caused by an invalid decodeURIComponent call.

How to fix this error: Cheque that the decodeURIComponent call at the error'southward line number gets correct input.

XMLHttpRequest cannot load http://some/url/. No 'Admission-Command-Let-Origin' header is nowadays on the requested resource

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

This error is e'er caused by the usage of XMLHttpRequest.

How to set up this fault: Ensure the request URL is correct and information technology respects the same-origin policy. A skillful style to find the offending code is to look at the URL in the error bulletin 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 11

Means the code called a function that y'all should not telephone call at the current land. Occurs usually with XMLHttpRequest, when attempting to phone call functions on it before it's ready.

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

In this case, you would get the error because the setRequestHeader part can simply exist called later calling xhr.open.

How to fix this error: Await at the code on the line pointed by the error and make sure it runs at the right time, or add whatsoever necessary calls before it (such every bit xhr.open up)

Decision

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

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

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

Nigh Jani Hartikainen

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

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

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