Chart.js Typeerror: Cannot Read Property 'getbasepixel' of Undefined

JavaScript Errors and How to Fix Them

JavaScript can be a nightmare to debug: Some errors it gives tin be very hard to empathise at outset, and the line numbers given aren't e'er helpful either. Wouldn't it be useful to take a list where y'all could look to find out what they hateful and how to fix them? Here you get!

Below is a list of the strange errors in JavaScript. Unlike browsers can give y'all different letters for the same mistake, so in that location are several unlike examples where applicable.

How to read errors?

Before the listing, let's quickly look at the structure of an mistake message. Understanding the structure helps sympathise the errors, and you lot'll have less problem if you encounter whatsoever errors not listed here.

A typical error from Chrome looks like this:

Uncaught TypeError: undefined is non a role

The structure of the mistake is as follows:

1. Uncaught TypeError: This part of the message is usually not very useful. Uncaught means the fault was not caught in a take hold of argument, and TypeError is the error's proper name.
2. undefined is non a function: 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 role.

Other webkit-based browsers, like Safari, requite errors in a like format to Chrome. Errors from Firefox are similar, simply do not ever include the kickoff part, and recent versions of Net Explorer also requite simpler errors than Chrome – but in this instance, simpler does non always mean improve.

At present onto the actual errors.

Uncaught TypeError: undefined is not a function

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

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

var foo = undefined; foo();

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

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

Since object properties that don't be are undefined by default, the to a higher place would effect in this error.

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

How to gear up this mistake: Ensure the function name is correct. With this error, the line number will usually point at the correct location.

Uncaught ReferenceError: Invalid left-hand 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 nearly common example of this fault is with if-clauses:

if(doSomething() = 'somevalue')

In this example, the programmer accidentally used a unmarried equals instead of ii. The bulletin "left-hand side in consignment" is referring to the part on the left side of the equals sign, so like you can see in the above case, the left-hand side contains something you can't assign to, leading to the mistake.

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 statement not supported

E'er caused by a circular 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 in a higher place example take a reference to each other, the resulting object cannot be converted into JSON.

How to prepare this error: Remove circular references like in the case from any objects y'all want to catechumen into JSON.

Unexpected token ;

Related errors: Expected ), missing ) after statement list

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

The token in this error 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 it difficult to fix.

• An error with [ ] { } ( ) is usually caused by a mismatching pair. Check that all your parentheses and brackets have a matching pair. In this example, line number volition often indicate to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this volition usually be correct.
• Unexpected ; is normally caused by having a ; within an object or assortment literal, or within the statement list of a function call. The line number will usually exist right for this case besides

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated String Literal, Invalid Line Terminator

A string literal is missing the closing quote.

How to fix this error: Ensure all strings take the correct closing quote.

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

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

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

var someVal = nothing; console.log(someVal.foo);

How to prepare this error: Ordinarily acquired by typos. Check that the variables used well-nigh the line number pointed by the fault are correctly named.

Uncaught TypeError: Cannot set holding 'foo' of cypher, Uncaught TypeError: Cannot set property 'foo' of undefined

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

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

var someVal = zilch; someVal.foo = 1;

How to fix this error: This too is usually acquired by typos. Check the variable names well-nigh the line the error points to.

Uncaught RangeError: Maximum call stack size exceeded

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

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

How to set up this error: Cheque recursive functions for bugs that could cause them to go on recursing forever.

Uncaught URIError: URI malformed

Related errors: URIError: malformed URI sequence

Caused by an invalid decodeURIComponent telephone call.

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

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

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

This fault is always caused by the usage of XMLHttpRequest.

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

InvalidStateError: An effort 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 yous should not call at the current state. Occurs usually 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 lot would get the error because the setRequestHeader role can but be called afterwards calling xhr.open up.

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

Conclusion

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

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

Desire to learn more about these errors and how to foreclose them? Detect Problems in JavaScript Automatically with ESLint.

About Jani Hartikainen

Jani Hartikainen has spent over 10 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 high quality code on his site.

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

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