Tutorial by Examples: er

NaN ("Not a Number") is a special value defined by the IEEE Standard for Floating-Point Arithmetic, which is used when a non-numeric value is provided but a number is expected (1 * "two"), or when a calculation doesn't have a valid number result (Math.sqrt(-1)). Any equality or ...

There are several PHP functions that accept user-defined callback functions as a parameter, such as: call_user_func(), usort() and array_map(). Depending on where the user-defined callback function was defined there are different ways to pass them: Procedural style: function square($number) { ...

Getters and setters allow you to define custom behaviour for reading and writing a given property on your class. To the user, they appear the same as any typical property. However, internally a custom function you provide is used to determine the value when the property is accessed (the getter), and...

If it's not already done in php.ini, error reporting can be set dynamically and should be set to allow most errors to be shown: Syntax int error_reporting ([ int $level ] ) Examples // should always be used prior to 5.4 error_reporting(E_ALL); // -1 will show every possible error, even whe...

try/catch try..catch blocks can be used to control the flow of a program where Exceptions may be thrown. They can be caught and handled gracefully rather than letting PHP stop when one is encountered: try { // Do a bunch of things... throw new Exception('My test exception!'); } catch (E...

Perl tries to do what you mean: print "Hello World\n"; The two tricky bits are the semicolon at the end of the line and the \n, which adds a newline (line feed). If you have a relatively new version of perl, you can use say instead of print to have the carriage return added automatical...

An unordered list can be created with the <ul> tag and each list item can be created with the <li> tag as shown by the example below: <ul> <li>Item</li> <li>Another Item</li> <li>Yet Another Item</li> </ul> This will produce a...

An ordered list can be created with the <ol> tag and each list item can be created with the <li> tag as in the example below: <ol> <li>Item</li> <li>Another Item</li> <li>Yet Another Item</li> </ol> This will produce a numbere...

One common pitfall when using dictionaries is to access a non-existent key. This typically results in a KeyError exception mydict = {} mydict['not there'] Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: 'not there' One way to avoid...

Right after you install Git, the first thing you should do is set your username and email address. From a shell, type: git config --global user.name "Mr. Bean" git config --global user.email mrbean@example.com git config is the command to get or set options --global means that the ...

To see the log in a prettier graph-like structure use: git log --decorate --oneline --graph sample output : * e0c1cea (HEAD -> maint, tag: v2.9.3, origin/maint) Git 2.9.3 * 9b601ea Merge branch 'jk/difftool-in-subdir' into maint |\ | * 32b8c58 difftool: use Git::* functions instead of...

The function rand() can be used to generate a pseudo-random integer value between 0 and RAND_MAX (0 and RAND_MAX included). srand(int) is used to seed the pseudo-random number generator. Each time rand() is seeded wih the same seed, it must produce the same sequence of values. It should only be see...

Here's a standalone random number generator that doesn't rely on rand() or similar library functions. Why would you want such a thing? Maybe you don't trust your platform's builtin random number generator, or maybe you want a reproducible source of randomness independent of any particular library ...

File descriptors like 0 and 1 are pointers. We change what file descriptors point to with redirection. >/dev/null means 1 points to /dev/null. First we point 1 (STDOUT) to /dev/null then point 2 (STDERR) to whatever 1 points to. # STDERR is redirect to STDOUT: redirected to /dev/null, # effect...

2 is STDERR. $ echo_to_stderr 2>/dev/null # echos nothing Definitions: echo_to_stderr is a command that writes "stderr" to STDERR echo_to_stderr () { echo stderr >&2 } $ echo_to_stderr stderr

Defines an <initially-hidden> custom element which hides its contents until a specified number of seconds have elapsed. const InitiallyHiddenElement = document.registerElement('initially-hidden', class extends HTMLElement { createdCallback() { this.revealTimeoutId = null; } at...

6 Exceptions are to synchronous code what rejections are to promise-based asynchronous code. If an exception is thrown in a promise handler, its error will be automatically caught and used to reject the promise instead. Promise.resolve(5) .then(result => { throw new Error("I ...

Runtime errors in JavaScript are instances of the Error object. The Error object can also be used as-is, or as the base for user-defined exceptions. It's possible to throw any type of value - for example, strings - but you're strongly encouraged to use Error or one of it's derivatives to ensure that...

GHC's OverloadedLists extension allows you to construct list-like data structures with the list literal syntax. This allows you to Data.Map like this: > :set -XOverloadedLists > import qualified Data.Map as M > M.lookup "foo" [("foo", 1), ("bar", 2)] Just ...

a = 1 - Math.abs(1 - a % 2); // This will throw an error if my arithmetic above is wrong. assert a >= 0 && a <= 1 : "Calculated value of " + a + " is outside of expected bounds"; return a;