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- Dictionaryundefined/ˌʌndɪˈfʌɪnd/
adjective
- 1. not clear or defined: "undefined areas of jurisdiction" Similar Opposite
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Feb 22, 2011 · The undefined value is a primitive value used when a variable has not been assigned a value. The null value is a primitive value that represents the null, empty, or non-existent reference. When you declare a variable through var and do not give it a value, it will have the value undefined.
Jan 14, 2021 · I assume you expect a number as you set the var to 0 when undefined: var getVariable = localStorage.getItem('value'); var setVariable = (typeof getVariable == 'number') ? getVariable : 0; In this case if getVariable is not a number (string, object, whatever), setVariable is set to 0. answered Jun 30, 2016 at 5:07.
May 7, 2009 · An undeclared variable (that is, one that doesn't exist) does not have a type - and so its type is undefined. I believe that the generally accepted way to test if something is undefined is . typeof var === 'undefined' rather than. var === undefined since if the variable does not exist, you cannot access it.
@IanGrainger: ECMAScript 5 (implemented in current versions of all browsers) mostly fixes this by making undefined an immutable property of the global object, so it's safer than it used to be. However, it is still possible to define a mutable variable called undefined within a function, so the problem hasn't entirely gone away. –
Oct 3, 2019 · return gallons; // ! } This way, you can use your function like this: int gallons = getGallons(wall); // now gallons is defined and you can use it: getHours(gallons); Analogously for the other functions and variables. Usually, it is not a good idea to mix logic (calculations) and output in the same function.
May 23, 2014 · 10. If you want to be able to test its 'undefined state', you should set it to None : variable = None. and test with. if variable is None: If you want to clean stuff, you can delete it, del variable but that should be task of the garbage collector. answered May 23, 2014 at 11:48. damienfrancois. 58.3k 9 109 122.
It's been nearly five years since this post was first made, and JavaScript has come a long way. In repeating the tests in the original post, I found no consistent difference between the following test methods: abc === undefined. abc === void 0. typeof abc == 'undefined'. typeof abc === 'undefined'.
Aug 26, 2008 · JavaScript has typeof which make it very easy to detect an undefined variable. Simply check if typeof whatever === 'undefined' and it will return a boolean. That's how the famous function isUndefined() in AngularJs v.1x is written: function isUndefined(value) {return typeof value === 'undefined';}
To check if a variable is undefined you will have to check if the variable is in the list of defined variables, using get_defined_vars(). There is no equivalent to JavaScript's undefined (which is what was shown in the question, no jQuery being used there). In the following example it will work the same way as JavaScript's undefined check.
Dec 10, 2012 · 162. undefined is not a valid JSON value, even though it is valid in javascript. A JSON value can be an object, array, number, string, true, false, or null. If you want a value to be undefined, just omit it entirely from the JSON. That way, when you try to read it after parse, it will be undefined.
