Typeerror: Cannot Read Property 'options' of Null Deepstream

JavaScript Errors and How to Set Them

JavaScript can be a nightmare to debug: Some errors it gives tin can exist very difficult to understand at first, and the line numbers given aren't always helpful either. Wouldn't it exist useful to take a list where you could wait to find out what they mean and how to set up them? Here you go!

Below is a list of the strange errors in JavaScript. Different browsers can give you dissimilar messages for the same error, so there are several different examples where applicative.

How to read errors?

Before the list, allow'due south quickly look at the construction of an error bulletin. Understanding the structure helps understand the errors, and you'll have less trouble if y'all run into whatsoever errors not listed here.

A typical mistake from Chrome looks like this:

Uncaught TypeError: undefined is not a function

The structure of the error is every bit follows:

1. Uncaught TypeError: This part of the bulletin is usually not very useful. Uncaught ways the mistake was not caught 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, y'all have to read them very literally. For case in this case it literally means that the code attempted to use undefined like it was a office.

Other webkit-based browsers, like Safari, give errors in a similar format to Chrome. Errors from Firefox are similar, just do not always include the first part, and recent versions of Internet Explorer besides give simpler errors than Chrome – just in this case, simpler does not always hateful improve.

Now onto the actual errors.

Uncaught TypeError: undefined is not a part

Related errors: number is not a function, object is not a office, cord is not a office, Unhandled Error: 'foo' is not a role, Function Expected

Occurs when attempting to telephone call a value similar a role, where the value is not a office. For example:

var foo = undefined; foo();

This mistake typically occurs if you are trying to call a part 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 above would result in this error.

The other variations such as "number is non a function" occur when attempting to telephone call a number like information technology was a office.

How to fix this error: Ensure the part proper noun is correct. With this mistake, the line number volition unremarkably indicate at the right 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 nigh common 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 office on the left side of the equals sign, so like you can see in the above example, the left-hand side contains something you can't assign to, leading to the mistake.

How to fix this mistake: Brand sure you're non 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: Non an acyclic Object, TypeError: cyclic object value, Circular reference in value argument 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 above case take a reference to each other, the resulting object cannot be converted into JSON.

How to ready this error: Remove circular references similar in the example from any objects you desire to convert into JSON.

Unexpected token ;

Related errors: Expected ), missing ) later on argument list

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

The token in this error can vary – information technology might say "Unexpected token ]" or "Expected {" etc.

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

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

Uncaught SyntaxError: Unexpected token ILLEGAL

Related errors: Unterminated Cord 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 zero, Uncaught TypeError: Cannot read property 'foo' of undefined

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

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

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

How to fix this error: Usually caused by typos. Check that the variables used virtually the line number pointed by the fault are correctly named.

Uncaught TypeError: Cannot set holding 'foo' of zero, Uncaught TypeError: Cannot set up 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 as if it was an object. For case:

var someVal = null; someVal.foo = 1;

How to prepare this error: This besides 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, likewise much recursion, Stack overflow

Unremarkably caused by a bug in program logic, causing space recursive part calls.

How to set this error: Bank check recursive functions for bugs that could cause them to keep 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 call at the error's line number gets correct 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 resources at http://some/url/

This error is ever caused by the usage of XMLHttpRequest.

How to fix this error: Ensure the request URL is right and it respects the same-origin policy. A good way to discover 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 use an object that is not, or is no longer, usable

Related errors: InvalidStateError, DOMException lawmaking eleven

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

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

In this case, you would become the error because the setRequestHeader part can but exist called afterwards calling xhr.open.

How to prepare this fault: Look at the code on the line pointed by the mistake and make sure it runs at the correct time, or add any necessary calls earlier information technology (such as xhr.open)

Conclusion

JavaScript has some of the nigh unhelpful errors I've seen, with the exception of the notorious Expected T_PAAMAYIM_NEKUDOTAYIM in PHP. With more than familiarity the errors start to make more than sense. Modern browsers as well help, equally they no longer requite the completely useless errors they used to.

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

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

Virtually Jani Hartikainen

Jani Hartikainen has spent over 10 years edifice 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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