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- Dictionaryundefined/ˌʌndɪˈfʌɪnd/
adjective
- 1. not clear or defined: "undefined areas of jurisdiction" Similar Opposite
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@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. –
Jan 14, 2021 · Yes, it can do that, but strictly speaking that will assign the default value if the retrieved value is falsey, as opposed to truly undefined. It would therefore not only match undefined but also null, false, 0, NaN, "" (but not "0"). If you want to set to default only if the variable is strictly undefined then the safest way is to write:
Oct 3, 2019 · C++ identifier is undefined. Ask Question Asked 5 years, 1 month ago. Modified 1 year, 3 months ago. Viewed 191k times 6 I'm new to C++ I don't und ...
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.
Jun 6, 2021 · Define undefined array key in php. Ask Question Asked 3 years, 5 months ago. Modified 3 years, 5 months ago. Viewed 4k times Part of PHP Collective ...
Apr 24, 2010 · function is_undefined(value) { var undefined_check; // instantiate a new variable which gets initialized to the real undefined value return value === undefined_check; } This works because when someone writes undefined = "foo" he only lets the name undefined reference to a new value, but he doesn't change the actual value of undefined.
Oct 13, 2015 · I'm trying to insert a record into MYSQL table using sequelize. Installed sequelize and mysql. npm install --save sequelize npm install --save mysql defined it in app.js var Sequelize = requ
May 23, 2014 · @DukeDougal We suggest using None instead, because the idea of an undefined variable is not "pythonic". Python programmers are very particular about how the language is used that's why PEP's were made. Pylint is what most python programmers use to check code syntax, and it will show an undefined variable as bad practice.
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.
Feb 22, 2011 · It's worth noting that while this comment was true in '11, with the advent of optional function params, emergence of type-checking systems like Flow, and pervasiveness of React (all of which treat undefined and null very differently), the old wisdom of generally using null rather than undefined no longer holds so strictly. undefined is actually preferable to null in many cases where you want ...
