Tutorial by Examples: l

SELECT PhoneNumber, Email, PreferredContact FROM Customers This statement will return the columns PhoneNumber, Email, and PreferredContact from all rows of the Customers table. Also the columns will be returned in the sequence in which they appear in the SELECT clause. The re...

The removeEventListener() method removes event handlers that have been attached with the addEventListener() method: element.removeEventListener("mousemove", myFunction); Everything (eventname, function, and options) in the removeEventListener must match the one set when adding the even...

One of the most commonly used events is waiting for the document to have loaded, including both script files and images. The load event on document is used for this. document.addEventListener('load', function() { console.log("Everything has now loaded!"); }); Sometimes you try to ...

Individual values of a hash are read and written using the [] and []= methods: my_hash = { length: 4, width: 5 } my_hash[:length] #=> => 4 my_hash[:height] = 9 my_hash #=> {:length => 4, :width => 5, :height => 9 } By default, accessing a key which has not been added t...

By default, attempting to lookup the value for a key which does not exist will return nil. You can optionally specify some other value to return (or an action to take) when the hash is accessed with a non-existent key. Although this is referred to as "the default value", it need not be a s...

The differences between null and undefined null and undefined share abstract equality == but not strict equality ===, null == undefined // true null === undefined // false They represent slightly different things: undefined represents the absence of a value, such as before an identifier/...

The json module contains functions for both reading and writing to and from unicode strings, and reading and writing to and from files. These are differentiated by a trailing s in the function name. In these examples we use a StringIO object, but the same functions would apply for any file-like obje...

For any iterable (for eg. a string, list, etc), Python allows you to slice and return a substring or sublist of its data. Format for slicing: iterable_name[start:stop:step] where, start is the first index of the slice. Defaults to 0 (the index of the first element) stop one past the last in...

A quick way to make a copy of an array (as opposed to assigning a variable with another reference to the original array) is: arr[:] Let's examine the syntax. [:] means that start, end, and slice are all omitted. They default to 0, len(arr), and 1, respectively, meaning that subarray that we are ...

An external CSS stylesheet can be applied to any number of HTML documents by placing a <link> element in each HTML document. The attribute rel of the <link> tag has to be set to "stylesheet", and the href attribute to the relative or absolute path to the stylesheet. While usin...

The background-color property sets the background color of an element using a color value or through keywords, such as transparent, inherit or initial. transparent, specifies that the background color should be transparent. This is default. inherit, inherits this property from its parent e...

Jsoup can be be used to easily extract all links from a webpage. In this case, we can use Jsoup to extract only specific links we want, here, ones in a h3 header on a page. We can also get the text of the links. Document doc = Jsoup.connect("http://stackoverflow.com").userAgent("Mozi...

Create a new file called hello.sh with the following content and give it executable permissions with chmod +x hello.sh. Execute/Run via: ./hello.sh #!/usr/bin/env bash # Note that spaces cannot be used around the `=` assignment operator whom_variable="World" # Use printf to sa...

a, b = 2, 3 a * b # = 6 import operator operator.mul(a, b) # = 6 Possible combinations (builtin types): int and int (gives an int) int and float (gives a float) int and complex (gives a complex) float and float (gives a float) float and complex (gives a comple...

By default, the math.log function calculates the logarithm of a number, base e. You can optionally specify a base as the second argument. import math import cmath math.log(5) # = 1.6094379124341003 # optional base argument. Default is math.e math.log(5, math.e) # = 1.6094379124341003 ...

Direction-Specific Properties CSS allows you to specify a given side to apply margin to. The four properties provided for this purpose are: margin-left margin-right margin-top margin-bottom The following code would apply a margin of 30 pixels to the left side of the selected div. View Resu...

You can include another Git repository as a folder within your project, tracked by Git: $ git submodule add https://github.com/jquery/jquery.git You should add and commit the new .gitmodules file; this tells Git what submodules should be cloned when git submodule update is run.

When you clone a repository that uses submodules, you'll need to initialize and update them. $ git clone --recursive https://github.com/username/repo.git This will clone the referenced submodules and place them in the appropriate folders (including submodules within submodules). This is equivale...

Anchors can be used to jump to specific tags on an HTML page. The <a> tag can point to any element that has an id attribute. To learn more about IDs, visit the documentation about Classes and IDs. Anchors are mostly used to jump to a subsection of a page and are used in conjunction with header...

Python provides string interpolation and formatting functionality through the str.format function, introduced in version 2.6 and f-strings introduced in version 3.6. Given the following variables: i = 10 f = 1.5 s = "foo" l = ['a', 1, 2] d = {'a': 1, 2: 'foo'} The following statem...