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How to check for an undefined or null variable in JavaScript?
...
A variable that has been declared but not initialized is undefined.
let foo;
if (foo) //evaluates to false because foo === undefined
Undefined properties , like someExistingObj.someUndefProperty. An undefined property doesn't yield an error and simply returns undefined, which, when converted t...
typeof for RegExp
...
You can use instanceof operator:
var t = /^foo(bar)?$/i;
alert(t instanceof RegExp);//returns true
In fact, that is almost the same as:
var t = /^foo(bar)?$/i;
alert(t.constructor == RegExp);//returns true
Keep in mind that as RegExp is not a primitive data type,...
Upgrade python in a virtualenv
... of Python version
Directions:
Let's say your existing project is named foo and is currently running Python 2 (mkproject -p python2 foo), though the commands are the same whether upgrading from 2.x to 3.x, 3.6.0 to 3.6.1, etc. I'm also assuming you're currently inside the activated virtual envir...
What is the difference between os.path.basename() and os.path.dirname()?
...rname(path) function returns the head of the path.
E.g.: The dirname of '/foo/bar/item' is '/foo/bar'.
The os.path.basename(path) function returns the tail of the path.
E.g.: The basename of '/foo/bar/item' returns 'item'
From: http://docs.python.org/2/library/os.path.html#os.path.basename
...
shortcut for creating a Map from a List in groovy?
... then the method collectEntries should suffice. For example
def names = ['Foo', 'Bar']
def firstAlphabetVsName = names.collectEntries {[it.charAt(0), it]} // [F:Foo, B:Bar]
But if you want a structure similar to a Multimap, in which there are multiple values per key, then you'd want to use the gr...
汇编语言超浓缩教程（汇编入门必备） - C/C++ - 清泛网 - 专注C/C++及内核技术
... D8-0E 81 C3 FE 53 89 5E FE ......k.....S.^.
1975:0170 8B C2 E8 FB FD 0B C0 75-09 8B 5E FE 8B 47 0C E8 .......u..^..G..
现在，我们来剖析另一个程序：由键盘输入任意字符串，然后显示出来。db 20指示DEBUG保留20h个未用的内存空间供缓冲区使用...
Python loop that also accesses previous and next values
...
This should do the trick.
foo = somevalue
previous = next_ = None
l = len(objects)
for index, obj in enumerate(objects):
if obj == foo:
if index > 0:
previous = objects[index - 1]
if index < (l - 1):
n...
Is JavaScript's “new” keyword considered harmful?
...ily mitigated - simply add a bit of code to the function itself:
function foo()
{
// if user accidentally omits the new keyword, this will
// silently correct the problem...
if ( !(this instanceof foo) )
return new foo();
// constructor logic follows...
}
Now you can have the ...
How do I override __getattr__ in Python without breaking the default behavior?
...ttributes in the instance that match the name. For instance, if you access foo.bar, then __getattr__ will only be called if foo has no attribute called bar. If the attribute is one you don't want to handle, raise AttributeError:
class Foo(object):
def __getattr__(self, name):
if some_pr...
SetUnhandledExceptionFilter and the C/C++ Runtime Library - C/C++ - 清泛网 - 专注IT技能提升
...ash!" << std::endl;
Bar();
}
virtual void Foo() = 0;
void Bar()
{
Foo();
}
};
struct D: public B
{
void Foo()
{
}
};
B* b = new D;
// Just to silence the warning C4...