NodeJs

To expand my knowledge and sharpen my skills, I have decided to dive into nodeJs. This is my buddle of Learning packs.

To Start, I had to install nodejs from the official site.

SOME LECTURE:

NodeJs is built on google chrome's javascript v8 engine. It is open source , cross platform and is capable of generating real time web applications. It is developed by Ryan Dahl with the team of other developers working at joyent in 2009. It's package ecosystem 'NPM' is the largest ecosystem of open source libraries in the world.

Running node:

Node is uses javascript and all node files uses the .js extention. To run node file we simply write node filename in any terminal.

NodeJs allows us to create serve allowing it serve different content types from our machine. It comes with built in method that allows us to create a server and as well listen to a port. Once listening and all configured correctly expected results are gotten at the console. While we used res.end() to send response, this only sends one response and then we need something like res.write() to be able to send multiple response.

Day Two - Fs Package

NodeJs comes with a built-in package known as fs which gives us access to the file system or the file I/O. The fs system can perform in synchronous or asynchronous manner. We import the fs system by require('fs');

To read from file

To read the content of the file we use the readFile() method which can be synchronous or asynchronous.

Write to file

We make use of the writeFile() method which can be synchronous or asynchronous.

Append to file

Sometimes we need to add new information to an existing file without change the already content in it. To achieve this we use the appendFile() method, can be synchronous or asynchronous as well.

Rename Files

The fs system all gives us the ability to rename a file through the rename() method. Can be synchronous or asynchronous as well.

Delete Files

Finally the fs module gives us access to delete file via the unlink() method. Like others it can be synchronous or asynchronous.

Day Three - Regular Expressions in nodejs

Regular expressions are sequence of characters that define a pattern in strings. We can employ in many areas such as validations and checking that give expression matches the desired format. We often refer to this as regex .

To create a regex

In node there are different ways we can create a regex, first can be enclosing the expression in /, second can be through the use of the node function regExp.

var reg = /ab*/;
//It will match a , ab, abb , abbbbbb , abbbbbbb and so on.
//But will not match b, bc, abc,aba , etc.

var reg = new RegExp('ab*');
//It will match a , ab, abb , abbbbbb , abbbbbbb and so on.
//But will not match b, bc, abc,aba , etc.

Modifiers

Regular expressions have some flags known as modifers that we can add to the expression to define the scope level. g - global scope i - case insensitive m - multiline match

Common Examples of Regular Expressions

1 - Finding Specific text using Regular expression: In this we shall be using the data.txt file and we shall be looking for the word man.

2 - Finding Number of tags using Regular expression: We will look through an html file and find the number of tags that was used in the file. We shall use the data.html file.

3 - Validating emails using regular expression : In this we are giving a email as input in order to find out whether it met all the contraints of being a valid one.The pattern will match the constraints such as @ (1 Occurrence) , domain is provided , sub-domain , etc. After matching , if the email is a valid one it will console "Valid" and "Please enter a valid email" if the email provided is not a valid one.

DennisDon678 / NodeJs