Ncaught Typeerror: Cannot Read Property 'bits' of Undefined Twitch

JavaScript Errors and How to Prepare Them

JavaScript can be a nightmare to debug: Some errors it gives tin can be very hard to sympathise at start, and the line numbers given aren't ever helpful either. Wouldn't it exist useful to have a list where you could look to notice out what they mean and how to fix them? Hither you go!

Below is a listing of the strange errors in JavaScript. Dissimilar browsers tin can give you lot unlike messages for the aforementioned error, so there are several different examples where applicative.

How to read errors?

Earlier the list, let's quickly look at the construction of an error message. Understanding the structure helps empathize the errors, and you'll have less trouble if y'all run into whatever errors not listed here.

A typical error from Chrome looks like this:

Uncaught TypeError: undefined is not a function

The structure of the error is equally follows:

1. Uncaught TypeError: This part of the message is commonly not very useful. Uncaught means the mistake was not caught in a catch statement, and TypeError is the error's name.
2. undefined is non a function: This is the message part. With error messages, yous have to read them very literally. For example in this instance it literally means that the code attempted to utilise undefined like information technology was a office.

Other webkit-based browsers, like Safari, give errors in a similar format to Chrome. Errors from Firefox are similar, but practise not always include the first part, and recent versions of Internet Explorer also give simpler errors than Chrome – simply in this case, simpler does non always mean amend.

Now onto the bodily errors.

Uncaught TypeError: undefined is not a part

Related errors: number is not a function, object is not a part, string is not a function, Unhandled Mistake: 'foo' is not a part, Part Expected

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

var foo = undefined; foo();

This error typically occurs if you are trying to call a part in an object, but yous typed the name incorrect.

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

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

The other variations such equally "number is non a part" occur when attempting to call a number like it was a function.

How to gear up this mistake: Ensure the part proper noun is correct. With this mistake, the line number volition usually point at the correct location.

Uncaught ReferenceError: Invalid left-hand side in consignment

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 most mutual example of this error is with if-clauses:

if(doSomething() = 'somevalue')

In this example, the developer accidentally used a single equals instead of two. The message "left-paw side in assignment" is referring to the part on the left side of the equals sign, so like you can see in the above instance, the left-hand side contains something you lot can't assign to, leading to the mistake.

How to fix this error: Make sure you're not attempting to assign values to office 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 statement not supported

Ever caused past 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 to a higher place instance have a reference to each other, the resulting object cannot exist converted into JSON.

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

Unexpected token ;

Related errors: Expected ), missing ) after argument list

The JavaScript interpreter expected something, simply 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 fix this mistake: Sometimes the line number with this error doesn't point to the correct place, making information technology hard to fix.

• An error with [ ] { } ( ) is normally caused by a mismatching pair. Check that all your parentheses and brackets have a matching pair. In this instance, line number will often point to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this will usually be correct.
• Unexpected ; is usually caused by having a ; inside an object or array literal, or within the argument listing of a function telephone call. The line number will usually be correct for this case also

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated Cord Literal, Invalid Line Terminator

A string literal is missing the endmost quote.

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

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

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

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

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

How to gear up this error: Unremarkably caused past typos. Check that the variables used about the line number pointed by the error are correctly named.

Uncaught TypeError: Cannot set up belongings '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 aught reference

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

var someVal = null; someVal.foo = 1;

How to prepare this mistake: This too is usually acquired past typos. Cheque the variable names nearly the line the fault points to.

Uncaught RangeError: Maximum call stack size exceeded

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

Usually caused past a issues in plan logic, causing infinite recursive part calls.

How to ready this error: Cheque 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 phone call at the fault's line number gets correct input.

XMLHttpRequest cannot load http://some/url/. No 'Access-Control-Let-Origin' header is present on the requested resource

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

This fault is always acquired past the usage of XMLHttpRequest.

How to fix this mistake: Ensure the request URL is right and it respects the same-origin policy. A good way to find the offending code is to expect at the URL in the mistake message and find it from your code.

InvalidStateError: An attempt was fabricated to use an object that is non, or is no longer, usable

Related errors: InvalidStateError, DOMException code 11

Means the code called a function that you should non call at the current state. Occurs normally with XMLHttpRequest, when attempting to 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 role tin only be called later on calling xhr.open.

How to fix this fault: Look at the lawmaking on the line pointed by the error and make sure information technology runs at the correct time, or add any necessary calls before it (such equally xhr.open up)

Conclusion

JavaScript has some of the most 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, as they no longer give the completely useless errors they used to.

What's the almost disruptive fault you lot've seen? Share the frustration in the comments!

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

Near Jani Hartikainen

Jani Hartikainen has spent over 10 years building spider web applications. His clients include companies like Nokia and hot super hole-and-corner startups. When non programming or playing games, Jani writes about JavaScript and loftier quality lawmaking on his site.

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

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