Typeerror Cannot Read Property of Null Viz Chart
JavaScript Errors and How to Fix Them
JavaScript tin be a nightmare to debug: Some errors it gives can be very difficult to empathise at kickoff, and the line numbers given aren't always helpful either. Wouldn't it be useful to have a list where y'all could await to detect out what they mean and how to fix them? Here you get!
Beneath is a list of the foreign errors in JavaScript. Different browsers tin can give you unlike messages for the aforementioned error, so there are several different examples where applicable.
How to read errors?
Before the list, let'southward quickly look at the structure of an fault message. Agreement the structure helps sympathize the errors, and you'll have less trouble if you come across any errors not listed here.
A typical error from Chrome looks like this:
Uncaught TypeError: undefined is non a function
The construction of the mistake is equally follows:
- Uncaught TypeError: This office of the message is commonly non very useful. Uncaught means the error was not caught in a
take hold ofstatement, andTypeErroris the error's name. - undefined is non a function: This is the bulletin office. With error messages, you accept to read them very literally. For example in this instance it literally means that the code attempted to utilize
undefinedlike it was a function.
Other webkit-based browsers, like Safari, give errors in a like format to Chrome. Errors from Firefox are similar, but do not e'er include the get-go office, and contempo versions of Internet Explorer as well give simpler errors than Chrome – merely in this case, simpler does not always mean better.
Now onto the actual errors.
Uncaught TypeError: undefined is not a role
Related errors: number is not a function, object is non a function, string is non a function, Unhandled Error: 'foo' is non a function, Role Expected
Occurs when attempting to call a value similar a function, where the value is not a function. For example:
var foo = undefined; foo();
This fault typically occurs if you are trying to call a part in an object, but you typed the proper name wrong.
var x = certificate.getElementByID('foo'); Since object properties that don't exist are undefined by default, the above would consequence in this error.
The other variations such as "number is non a function" occur when attempting to call a number like it was a office.
How to set up this error: Ensure the office name is correct. With this error, the line number volition normally point 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'
Caused by attempting to assign a value to something that cannot be assigned to.
The nearly mutual example of this error is with if-clauses:
if(doSomething() = 'somevalue')
In this example, the programmer accidentally used a single equals instead of two. The message "left-hand side in consignment" is referring to the part on the left side of the equals sign, then like you tin see in the above example, the left-hand side contains something you can't assign to, leading to the error.
How to fix this error: Brand certain 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 not supported
E'er acquired by a round 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 have a reference to each other, the resulting object cannot be converted into JSON.
How to fix this error: Remove circular references like in the instance from any objects you desire to convert into JSON.
Unexpected token ;
Related errors: Expected ), missing ) later statement listing
The JavaScript interpreter expected something, but information technology wasn't there. Typically caused by mismatched parentheses or brackets.
The token in this fault can vary – it might say "Unexpected token ]" or "Expected {" etc.
How to fix this fault: Sometimes the line number with this error doesn't betoken to the correct identify, 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 instance, line number will often point to something else than the trouble character
- Unexpected / is related to regular expressions. The line number for this will usually be correct.
- Unexpected ; is usually caused past having a ; inside an object or array literal, or within the argument listing of a function phone call. The line number will usually exist correct for this case as well
Uncaught SyntaxError: Unexpected token ILLEGAL
Related errors: Unterminated String Literal, Invalid Line Terminator
A cord literal is missing the closing quote.
How to set up this error: Ensure all strings take the correct endmost quote.
Uncaught TypeError: Cannot read belongings 'foo' of null, Uncaught TypeError: Cannot read property 'foo' of undefined
Related errors: TypeError: someVal is zippo, Unable to go property 'foo' of undefined or nil reference
Attempting to read nil or undefined as if it was an object. For example:
var someVal = null; panel.log(someVal.foo);
How to set up this fault: Ordinarily caused past typos. Check that the variables used almost the line number pointed by the error are correctly named.
Uncaught TypeError: Cannot ready property 'foo' of null, Uncaught TypeError: Cannot ready property 'foo' of undefined
Related errors: TypeError: someVal is undefined, Unable to set property 'foo' of undefined or null reference
Attempting to write nothing or undefined as if it was an object. For case:
var someVal = null; someVal.foo = ane;
How to fix this error: This besides is commonly acquired by typos. Bank check the variable names near the line the error points to.
Uncaught RangeError: Maximum phone call stack size exceeded
Related errors: Uncaught exception: RangeError: Maximum recursion depth exceeded, too much recursion, Stack overflow
Unremarkably acquired by a bug in program logic, causing space recursive office calls.
How to set up this error: Bank check recursive functions for bugs that could crusade them to go on recursing forever.
Uncaught URIError: URI malformed
Related errors: URIError: malformed URI sequence
Caused past an invalid decodeURIComponent telephone call.
How to fix this fault: Check that the decodeURIComponent telephone call at the mistake's line number gets right input.
XMLHttpRequest cannot load http://some/url/. No 'Access-Control-Allow-Origin' header is nowadays on the requested resource
Related errors: Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://some/url/
This mistake is always acquired 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 good way to notice the offending code is to look at the URL in the mistake message and find it from your lawmaking.
InvalidStateError: An effort was made to use an object that is not, or is no longer, usable
Related errors: InvalidStateError, DOMException code eleven
Means the code called a function that y'all should not call at the current state. Occurs usually with XMLHttpRequest, when attempting to call functions on it before it's prepare.
var xhr = new XMLHttpRequest(); xhr.setRequestHeader('Some-Header', 'val'); In this case, y'all would get the error because the setRequestHeader function tin can just be chosen after calling xhr.open.
How to fix this error: Look at the lawmaking on the line pointed by the error and make sure information technology runs at the correct time, or add together whatever necessary calls before 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 familiarity the errors commencement to make more sense. Modern browsers also help, every bit they no longer give the completely useless errors they used to.
What'southward the about confusing error you've seen? Share the frustration in the comments!
Want to learn more about these errors and how to foreclose them? Detect Problems in JavaScript Automatically with ESLint.
Well-nigh 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 near JavaScript and high quality code on his site.
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Source: https://davidwalsh.name/fix-javascript-errors
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