JavaScript check if variable exists (is defined/initialized)
You want the typeof operator. Specifically: if (typeof variable !== ‘undefined’) { // the variable is defined }
variables
Static vs class functions/variables in Swift classes?
static and class both associate a method with a class, rather than an instance of a class. The difference is that subclasses can override class methods; they cannot override static methods. class properties will theoretically function in the same way (subclasses can override them), but they’re not possible in Swift yet.
Is there a better way of writing v = (v == 0 ? 1 : 0); [closed]
You can simply use: v = 1 – v; This of course assumes that the variable is initialised properly, i.e. that it only has the value 0 or 1. Another method that is shorter but uses a less common operator: v ^= 1; Edit: To be clear; I never approached this question as code golf, … Read more
Determine if variable is defined in Python [duplicate]
try: thevariable except NameError: print(“well, it WASN’T defined after all!”) else: print(“sure, it was defined.”)
MySQL: @variable vs. variable. What’s the difference?
MySQL has a concept of user-defined variables. They are loosely typed variables that may be initialized somewhere in a session and keep their value until the session ends. They are prepended with an @ sign, like this: @var You can initialize this variable with a SET statement or inside a query: SET @var = 1 … Read more
Create timestamp variable in bash script
If you want to get unix timestamp, then you need to use: timestamp=$(date +%s) %T will give you just the time; same as %H:%M:%S (via http://www.cyberciti.biz/faq/linux-unix-formatting-dates-for-display/)
How to use a variable for a key in a JavaScript object literal?
{ thetop : 10 } is a valid object literal. The code will create an object with a property named thetop that has a value of 10. Both the following are the same: obj = { thetop : 10 }; obj = { “thetop” : 10 }; In ES5 and earlier, you cannot use a … Read more
Length of string in bash
To get the length of a string stored in a variable, say: myvar=”some string” size=${#myvar} To confirm it was properly saved, echo it: $ echo “$size” 11
Is it possible to print a variable’s type in standard C++?
C++11 update to a very old question: Print variable type in C++. The accepted (and good) answer is to use typeid(a).name(), where a is a variable name. Now in C++11 we have decltype(x), which can turn an expression into a type. And decltype() comes with its own set of very interesting rules. For example decltype(a) … Read more
Expansion of variables inside single quotes in a command in Bash
Inside single quotes everything is preserved literally, without exception. That means you have to close the quotes, insert something, and then re-enter again. ‘before'”$variable”‘after’ ‘before'”‘”‘after’ ‘before’\”after’ Word concatenation is simply done by juxtaposition. As you can verify, each of the above lines is a single word to the shell. Quotes (single or double quotes, depending … Read more