Uncaught Typeerror: Cannot Read Property 'data' of Undefined Kendo Grid Data

JavaScript Errors and How to Fix Them

JavaScript can be a nightmare to debug: Some errors it gives tin can exist very hard to understand at first, and the line numbers given aren't always helpful either. Wouldn't it exist useful to have a list where you could look to discover out what they mean and how to gear up them? Hither you get!

Below is a list of the strange errors in JavaScript. Different browsers tin give you different messages for the aforementioned error, then at that place are several unlike examples where applicable.

How to read errors?

Before the list, let'due south quickly await at the structure of an error message. Understanding the structure helps empathise the errors, and you'll have less trouble if you run into any errors not listed here.

A typical error from Chrome looks like this:

Uncaught TypeError: undefined is not a part

The structure of the error is every bit follows:

1. Uncaught TypeError: This role of the message is usually not very useful. Uncaught means the fault was not caught in a catch statement, and TypeError is the fault'southward name.
2. undefined is non a function: This is the bulletin function. With error messages, yous take to read them very literally. For example in this case information technology literally means that the code attempted to utilize undefined similar it was a office.

Other webkit-based browsers, like Safari, give errors in a like format to Chrome. Errors from Firefox are like, but practice not e'er include the showtime part, and recent versions of Internet Explorer also give simpler errors than Chrome – but in this case, simpler does not always mean improve.

Now onto the actual errors.

Uncaught TypeError: undefined is not a office

Related errors: number is not a part, object is not a function, string is not a function, Unhandled Error: '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, but you typed the name wrong.

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

Since object properties that don't exist are undefined by default, the higher up would consequence in this mistake.

The other variations such every bit "number is not a role" occur when attempting to telephone 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 usually point at the correct location.

Uncaught ReferenceError: Invalid left-paw 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 most mutual case of this mistake is with if-clauses:

if(doSomething() = 'somevalue')

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

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

Uncaught TypeError: Converting round construction to JSON

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

Always 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 above example have 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 any objects y'all want to convert into JSON.

Unexpected token ;

Related errors: Expected ), missing ) afterwards argument list

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

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

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

• An mistake with [ ] { } ( ) is usually acquired by a mismatching pair. Check that all your parentheses and brackets take a matching pair. In this case, line number will often point to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this will commonly be right.
• Unexpected ; is usually caused by having a ; inside an object or assortment literal, or within the argument list of a function call. The line number volition unremarkably 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 closing quote.

How to fix this error: Ensure all strings have the correct endmost quote.

Uncaught TypeError: Cannot read property 'foo' of null, Uncaught TypeError: Cannot read property 'foo' of undefined

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

Attempting to read naught or undefined every bit if it was an object. For example:

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

How to fix this mistake: Normally acquired by typos. Check that the variables used nearly the line number pointed past the mistake are correctly named.

Uncaught TypeError: Cannot gear up property 'foo' of cipher, Uncaught TypeError: Cannot prepare property 'foo' of undefined

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

Attempting to write cypher or undefined as if it was an object. For instance:

var someVal = zip; someVal.foo = 1;

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 telephone call stack size exceeded

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

Unremarkably caused by a bug in programme logic, causing space recursive role calls.

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

Uncaught URIError: URI malformed

Related errors: URIError: malformed URI sequence

Acquired by an invalid decodeURIComponent call.

How to fix this error: Bank check that the decodeURIComponent telephone call at the error'south line number gets correct input.

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

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

This mistake is always caused by the usage of XMLHttpRequest.

How to fix this error: Ensure the asking URL is right and it respects the same-origin policy. A adept way to discover the offending lawmaking is to expect at the URL in the error message and find it from your code.

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 you lot should not phone call at the electric current state. Occurs normally with XMLHttpRequest, when attempting to telephone call functions on information technology before it'due south ready.

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

In this example, you would get the fault because the setRequestHeader function can only be called after calling xhr.open.

How to set up this error: Look at the code on the line pointed by the error and make certain information technology runs at the right fourth dimension, or add whatever necessary calls before it (such equally xhr.open up)

Determination

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 brand more sense. Modern browsers as well help, equally they no longer give the completely useless errors they used to.

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

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

Well-nigh Jani Hartikainen

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

codeutopia.netjhartikainenPosts

boswellexhavy.blogspot.com

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

Share this post