Check For Reference Error Javascript
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here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers reference error is not defined javascript or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x referenceerror function is not defined Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it referenceerror variable is not defined only takes a minute: Sign up How can I compare a non-existing JavaScript object to undefined without getting a Reference Error? up vote 14 down vote favorite 5 I want to boolean to come out of this expression (task ===
Javascript Referenceerror
undefined); where task is arbitrary and doesn’t appear in the code at all. However, when I run this in rhino, I get a reference Error. I WANT TRUE Why don’t I get true? I want to check if a particular variable has been defined. How do I do it then if this doesn't work? javascript referenceerror share|improve this question edited Jul 8 '12 at 21:02 asked Jul 8 '12 at 2:43 Fawkes5 316410 add a comment| 2 Answers 2 active referenceerror $ is not defined jquery oldest votes up vote 35 down vote accepted Use this: (typeof task === "undefined") When you use (task === undefined), Javascript needs to find the value of task to see if it is the same as undefined, but it can't look up the name because it doesn't exist, giving you the reference error. typeof is special in that it can safely return the type of a name that doesn't exist. share|improve this answer answered Jul 8 '12 at 2:44 Ned Batchelder 178k31338493 Thank you! Why doesn’t JavaScript just declare task undefined, since it is literally undefined? –Fawkes5 Jul 8 '12 at 2:48 As I mentioned, you can't use the name task if it is undefined, it will raise an exception as you have seen. typeof is special. And Javascript did declare it undefined, it did it by raising the error! –Ned Batchelder Jul 8 '12 at 2:49 @Fawkes5: there's a difference between "variable exists but has value undefined" and "variable doesn't exist at all". –nnnnnn Jul 8 '12 at 2:50 thanks nnnnnn. Why is there a difference? –Fawkes5 Jul 8 '12 at 3:01 1 Because undefined is an actual value, which is evaluated as false. If you haven't declared the variable first like var foo; then the variable doesn't have an undefined value assigned to it, therefor you have to check if it's type is undefined to really check i
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Javascript Function Is Not Defined
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Javascript Not Undefined
Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Why does an undefined variable in Javascript sometimes evaluate http://stackoverflow.com/questions/11380283/how-can-i-compare-a-non-existing-javascript-object-to-undefined-without-getting to false and sometimes throw an uncaught ReferenceError? up vote 15 down vote favorite 5 Everything I've ever read indicates that in Javascript, the boolean value of an undefined variable is False. I've used code like this hundreds of times: if (!elem) { ... } with the intent that if "elem" is undefined, the code in the block will execute. It usually works, but on occasion the browser http://stackoverflow.com/questions/9981104/why-does-an-undefined-variable-in-javascript-sometimes-evaluate-to-false-and-som will throw an error complaining about the undefined reference. This seems so basic, but I can't find the answer. Is it that there's a difference between a variable that has not been defined and one that has been defined but which has a value of undefined? That seems completely unintuitive. javascript share|improve this question asked Apr 2 '12 at 17:42 Gullbyrd 742914 Just came here and want to leave a comment about 'hoisting'. If you declare the variable elem after your check and in the same function (scope) you will have a value of undefined from top of the function until you pass some value to it. –loveNoHate Jan 23 '14 at 7:59 add a comment| 8 Answers 8 active oldest votes up vote 20 down vote accepted What is a ReferenceError? As defined by ECMAScript 5, a ReferenceError indicates that an invalid reference has been detected. That doesn't say much by itself, so let's dig a little deeper. Leaving aside strict mode, a ReferenceError occurs when the scripting engine is instructed to get the value of a reference that it cannot resolve the base value for: A Reference is a resolved name binding. A Reference consists of thre
/ 5 CommentsTwo Solutions for "JavaScript Reference Error Is Not Defined"If you're working on any type of web site or web application that has any other dependencies either for its front-end framework - such as Bootstrap and Foundation - or from the site's foundation - such https://tommcfarlin.com/javascript-reference-error-is-not-defined/ as Rails or WordPress - there's a chance that your own JavaScript sources may result in the following:Reference Error [variable] is not defined.In some cases, this can be simply referring to a variable that isn't defined (perhaps the most popular is when jQuery's $ function has been dereferenced and you're trying to use $) and simply needs a definition.But, in other is not cases, there are times where it may not be as simple."JavaScript Reference Error is Not Defined"As mentioned, there are times in which simply defining a variable will resolve the issue. For example, given the example with jQuery above, we can make a call to noConflict() to restore the variable.Old references of $ are saved during jQuery initialization; noConflict() simply restores them.But that's getting beyond the point of is not defined this article.The thing is, simply restoring a variable or giving it a definition especially when it's related to a third-party dependency is not as easy.Instead, the problem can usually be resolved in one of two ways.1. Load the Libraries in Proper OrderArguably, the most popular reason for seeing a ReferenceError has to do with the fact that our script is referencing a variable that has yet to be defined.To fix this, it's generally a problem of the files being loaded out of order and this is especially true if the error is being thrown in the context of a site or web application that has its own libraries, then the scripts are probably loading later than your own.This means that either the scripts are placed after yours in the head element of the page or they are being loaded in the footer of the page. If that's the case, most frameworks and applications provide an API for setting the order in which files are loaded, setting dependencies, and then defining where, in the page, they are loaded.2. Leverage Undefined ValuesAnother more slightly involved example involves ca