Ncaught Typeerror: Cannot Read Property 'call' of Undefined
JavaScript Errors and How to Fix Them
JavaScript can exist a nightmare to debug: Some errors it gives can be very hard to understand at first, and the line numbers given aren't always helpful either. Wouldn't it be useful to take a list where you could look to observe out what they mean and how to fix them? Here you go!
Beneath is a list of the foreign errors in JavaScript. Different browsers tin give you lot different messages for the same mistake, so there are several different examples where applicable.
How to read errors?
Before the list, let's speedily look at the structure of an error message. Understanding the structure helps empathize the errors, and you'll have less trouble if you come across whatever errors not listed hither.
A typical error from Chrome looks like this:
Uncaught TypeError: undefined is not a function
The structure of the mistake is as follows:
- Uncaught TypeError: This part of the message is usually not very useful. Uncaught means the mistake was not defenseless in a
catchstatement, andTypeErroris the fault's name. - undefined is not a part: This is the message function. With error messages, you have to read them very literally. For case in this case it literally ways that the code attempted to use
undefinedlike it was a function.
Other webkit-based browsers, like Safari, give errors in a like format to Chrome. Errors from Firefox are like, but do not ever include the start role, and recent versions of Internet Explorer likewise give simpler errors than Chrome – but in this instance, simpler does not ever hateful improve.
At present onto the actual errors.
Uncaught TypeError: undefined is not a office
Related errors: number is not a office, object is not a function, cord is not a function, Unhandled Mistake: 'foo' is not a function, Office Expected
Occurs when attempting to phone call a value similar a role, where the value is not a role. For case:
var foo = undefined; foo();
This error typically occurs if y'all are trying to phone call a function in an object, only you typed the name incorrect.
var 10 = certificate.getElementByID('foo'); Since object properties that don't be are undefined by default, the above would result in this mistake.
The other variations such equally "number is not a function" occur when attempting to phone call a number like it was a function.
How to ready this error: Ensure the function proper noun is correct. With this fault, the line number will unremarkably point at the correct location.
Uncaught ReferenceError: Invalid left-hand 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 most 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 bulletin "left-hand side in consignment" is referring to the part on the left side of the equals sign, so like y'all tin can see in the to a higher place example, the left-manus side contains something y'all can't assign to, leading to the fault.
How to fix this error: Make sure y'all're not attempting to assign values to role 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 non supported
Always acquired past a round 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 instance have a reference to each other, the resulting object cannot exist converted into JSON.
How to ready this mistake: Remove circular references like in the example from any objects yous want to catechumen into JSON.
Unexpected token ;
Related errors: Expected ), missing ) subsequently argument list
The JavaScript interpreter expected something, simply it 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 error doesn't signal to the correct place, making it difficult to ready.
- An error with [ ] { } ( ) is usually caused by a mismatching pair. Cheque 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 usually be correct.
- Unexpected ; is unremarkably acquired by having a ; inside an object or assortment literal, or inside the statement list of a office call. The line number will usually exist correct for this case besides
Uncaught SyntaxError: Unexpected token ILLEGAL
Related errors: Unterminated String Literal, Invalid Line Terminator
A string literal is missing the endmost quote.
How to fix this error: Ensure all strings have the right closing quote.
Uncaught TypeError: Cannot read property 'foo' of null, Uncaught TypeError: Cannot read holding 'foo' of undefined
Related errors: TypeError: someVal is nil, 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; console.log(someVal.foo);
How to fix this fault: Normally acquired past typos. Bank check that the variables used about the line number pointed by the error are correctly named.
Uncaught TypeError: Cannot set property 'foo' of aught, Uncaught TypeError: Cannot set property 'foo' of undefined
Related errors: TypeError: someVal is undefined, Unable to ready holding 'foo' of undefined or null reference
Attempting to write null or undefined as if it was an object. For example:
var someVal = null; someVal.foo = 1;
How to ready this fault: This too is normally caused by typos. Bank check the variable names nigh the line the mistake points to.
Uncaught RangeError: Maximum call stack size exceeded
Related errors: Uncaught exception: RangeError: Maximum recursion depth exceeded, besides much recursion, Stack overflow
Usually acquired past a issues in program logic, causing infinite recursive function calls.
How to fix this error: Check 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 telephone call.
How to fix this fault: Check that the decodeURIComponent telephone call at the error's line number gets correct input.
XMLHttpRequest cannot load http://some/url/. No 'Admission-Control-Allow-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 fault is always caused by the usage of XMLHttpRequest.
How to fix this fault: Ensure the request URL is right and it respects the same-origin policy. A skillful style to find the offending code is to wait at the URL in the error message and find it from your code.
InvalidStateError: An attempt was made to employ an object that is not, or is no longer, usable
Related errors: InvalidStateError, DOMException lawmaking eleven
Means the lawmaking called a role that you should not call at the current state. Occurs commonly with XMLHttpRequest, when attempting to call functions on it earlier information technology's ready.
var xhr = new XMLHttpRequest(); xhr.setRequestHeader('Some-Header', 'val'); In this case, you would become the mistake because the setRequestHeader function tin just be chosen afterwards calling xhr.open up.
How to fix this error: Look at the code on the line pointed past the error and make certain it runs at the correct fourth dimension, or add any necessary calls earlier it (such as xhr.open up)
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 than familiarity the errors first to make more sense. Modern browsers also aid, equally they no longer give the completely useless errors they used to.
What's the most confusing fault y'all've seen? Share the frustration in the comments!
Want to acquire more than about these errors and how to prevent them? Detect Problems in JavaScript Automatically with ESLint.
About Jani Hartikainen
Jani Hartikainen has spent over 10 years building web applications. His clients include companies similar 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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Ncaught Typeerror: Cannot Read Property 'call' of Undefined
Source: https://davidwalsh.name/fix-javascript-errors