Eslint Cannot Read Property 'range' of Null

JavaScript Errors and How to Fix Them

JavaScript can exist a nightmare to debug: Some errors it gives can 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 discover out what they mean and how to prepare them? Here yous get!

Beneath is a listing of the strange errors in JavaScript. Different browsers tin give you different messages for the same fault, so there are several unlike examples where applicable.

How to read errors?

Before the list, let'south rapidly expect at the construction of an error bulletin. Agreement the structure helps understand the errors, and y'all'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 not a function

The structure of the error is as follows:

1. Uncaught TypeError: This function of the message is commonly not very useful. Uncaught means the error was not caught in a grab statement, and TypeError is the fault's name.
2. undefined is non a function: This is the bulletin part. With error messages, you take to read them very literally. For example in this case it literally means that the code attempted to use undefined similar it was a function.

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

Now onto the actual errors.

Uncaught TypeError: undefined is not a function

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

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

var foo = undefined; foo();

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

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

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

The other variations such every bit "number is not a function" occur when attempting to call a number like it was a function.

How to gear up this error: Ensure the role name is right. With this fault, the line number will unremarkably indicate at the correct location.

Uncaught ReferenceError: Invalid left-mitt 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 common case of this mistake is with if-clauses:

if(doSomething() = 'somevalue')

In this instance, the programmer accidentally used a single equals instead of ii. The message "left-mitt side in assignment" is referring to the part on the left side of the equals sign, so like you can see in the in a higher place example, the left-hand side contains something y'all can't assign to, leading to the error.

How to fix this error: Make certain you're not attempting to assign values to part results or to the this keyword.

Uncaught TypeError: Converting round 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

Always caused past a circular 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 to a higher place example have a reference to each other, the resulting object cannot be converted into JSON.

How to fix this error: Remove round references like in the example from whatsoever objects y'all want to convert into JSON.

Unexpected token ;

Related errors: Expected ), missing ) after statement listing

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

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

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

• An fault with [ ] { } ( ) is usually caused by a mismatching pair. Cheque that all your parentheses and brackets accept a matching pair. In this case, line number will often point to something else than the problem grapheme
• Unexpected / is related to regular expressions. The line number for this will ordinarily be correct.
• Unexpected ; is usually caused past having a ; inside an object or array literal, or within the argument list of a function call. The line number will usually be correct for this case likewise

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated String Literal, Invalid Line Terminator

A string literal is missing the closing quote.

How to prepare this error: Ensure all strings have the correct closing quote.

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

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

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

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

How to fix this error: Normally caused past typos. Check that the variables used near the line number pointed past the error are correctly named.

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

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

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

var someVal = zippo; someVal.foo = 1;

How to fix this error: This likewise is usually caused by typos. Check the variable names near the line the error points to.

Uncaught RangeError: Maximum call stack size exceeded

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

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

How to fix this mistake: 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 prepare this error: Bank check that the decodeURIComponent call at the error'south 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: Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://some/url/

This error is always caused by the usage of XMLHttpRequest.

How to set up this fault: Ensure the asking URL is correct and it respects the aforementioned-origin policy. A good way to notice the offending code is to look at the URL in the error message and discover it from your code.

InvalidStateError: An endeavor was made to utilise an object that is not, or is no longer, usable

Related errors: InvalidStateError, DOMException lawmaking eleven

Means the code called a role that you should not 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 mistake because the setRequestHeader part can simply be chosen after calling xhr.open up.

How to gear up this error: Look at the code on the line pointed by the fault and make sure it runs at the correct fourth dimension, or add any necessary calls before it (such equally xhr.open)

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. Modern browsers besides help, as they no longer give the completely useless errors they used to.

What's the virtually confusing error yous've seen? Share the frustration in the comments!

Want to larn more nigh these errors and how to foreclose them? Detect Problems in JavaScript Automatically with ESLint.

About Jani Hartikainen

Jani Hartikainen has spent over ten years building web applications. His clients include companies like Nokia and hot super secret startups. When non 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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