Typeerror: Cannot Read Property 'image' of Undefined

JavaScript Errors and How to Fix Them

JavaScript tin can be a nightmare to debug: Some errors it gives can be very difficult to sympathize at first, and the line numbers given aren't ever helpful either. Wouldn't information technology be useful to have a list where you lot could look to find out what they hateful and how to prepare them? Hither yous get!

Below is a list of the foreign errors in JavaScript. Different browsers tin requite you unlike messages for the same mistake, so there are several different examples where applicable.

How to read errors?

Earlier the listing, let'due south quickly look at the structure of an error bulletin. Understanding the structure helps empathize the errors, and yous'll have less trouble if you run across any errors not listed here.

A typical error from Chrome looks similar this:

Uncaught TypeError: undefined is non a function

The construction of the error is equally follows:

1. Uncaught TypeError: This part of the message is usually non very useful. Uncaught means the error was not defenseless in a catch statement, and TypeError is the error's name.
2. undefined is not a part: This is the bulletin part. With error messages, you have to read them very literally. For example in this case information technology literally means that the code attempted to apply undefined like it was a function.

Other webkit-based browsers, similar Safari, give errors in a similar format to Chrome. Errors from Firefox are similar, but do not always include the starting time function, and contempo versions of Internet Explorer also give simpler errors than Chrome – only in this instance, 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 non a function, Unhandled Error: 'foo' is not a office, Function Expected

Occurs when attempting to phone call a value like a function, where the value is non a office. For example:

var foo = undefined; foo();

This error typically occurs if y'all are trying to call a function in an object, but yous typed the name wrong.

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

Since object backdrop that don't exist are undefined past default, the above would outcome in this mistake.

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

How to gear up this error: Ensure the function proper 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'

Acquired past attempting to assign a value to something that cannot be assigned to.

The nigh common case 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-mitt side in assignment" is referring to the part on the left side of the equals sign, so like yous can come across in the above instance, the left-hand side contains something y'all tin can't assign to, leading to the error.

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

Uncaught TypeError: Converting circular construction to JSON

Related errors: Uncaught exception: TypeError: JSON.stringify: Non an acyclic Object, TypeError: cyclic object value, Circular reference in value statement not 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 ready this error: Remove circular references like in the case from any objects you want to catechumen into JSON.

Unexpected token ;

Related errors: Expected ), missing ) after statement list

The JavaScript interpreter expected something, but 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 set up this error: Sometimes the line number with this mistake doesn't indicate to the correct place, making it hard to prepare.

• An error with [ ] { } ( ) is commonly caused past a mismatching pair. Check that all your parentheses and brackets accept a matching pair. In this instance, line number will ofttimes point to something else than the problem character
• Unexpected / is related to regular expressions. The line number for this volition usually be correct.
• Unexpected ; is usually caused past having a ; within an object or assortment literal, or inside the argument list of a function call. The line number will commonly be correct for this case as 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 belongings 'foo' of nada, Uncaught TypeError: Cannot read holding 'foo' of undefined

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

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

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

How to set up this error: Usually caused by typos. Check that the variables used near the line number pointed by the error are correctly named.

Uncaught TypeError: Cannot set property 'foo' of zilch, Uncaught TypeError: Cannot set belongings 'foo' of undefined

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

Attempting to write null or undefined every bit if it was an object. For case:

var someVal = zip; someVal.foo = i;

How to set up this error: This too is usually acquired past 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 programme logic, causing infinite recursive function calls.

How to set up 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 past an invalid decodeURIComponent call.

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

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

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

This mistake is ever caused by the usage of XMLHttpRequest.

How to ready this error: Ensure the request URL is correct and it respects the aforementioned-origin policy. A adept fashion to find the offending code is to await at the URL in the error message and find it from your code.

InvalidStateError: An try was fabricated to use an object that is not, or is no longer, usable

Related errors: InvalidStateError, DOMException code xi

Means the code chosen a function that you lot should not telephone call at the electric current state. Occurs usually with XMLHttpRequest, when attempting to phone call functions on it before it's ready.

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

In this case, you would go the error because the setRequestHeader role can only be called subsequently calling xhr.open.

How to gear up this error: Look at the code on the line pointed by the error and brand sure it runs at the right time, or add any necessary calls earlier it (such as xhr.open)

Conclusion

JavaScript has some of the near 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 than sense. Modernistic browsers as well help, as they no longer give the completely useless errors they used to.

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

Desire to learn more most these errors and how to forbid them? Detect Bug in JavaScript Automatically with ESLint.

Almost Jani Hartikainen

Jani Hartikainen has spent over x years building web applications. His clients include companies like Nokia and hot super cloak-and-dagger startups. When non programming or playing games, Jani writes nearly JavaScript and high quality code on his site.

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