JS & TS on My Notes

JS & ES Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

The most unpredictable keyword and feature#

You may already guessed what I am talking about. Yes, thethis keyword. It is not only a powerful feature, but also often misinterpreted keyword.

In JavaScript, we also have this concept inside a Function constructor when it is invoked using the “new” keyword, however it is not the only rule and “this” can often refer to a different object from a different execution context.

JS & ES Note - 2

Mon, 01 Jan 0001 00:00:00 +0000

The equal operator doesn’t always mean equivalent#

Have you got confused by the equal or not equal expression in the JavaScript? I will say you are definitely not the only one. Even many senior developers come from back-end programming background, they all scratch the head to find out why the equal or not-equal expression doesn’t work as they expect. The truth is those expression are really different from other programming language.

JS & ES Note - 3

Mon, 01 Jan 0001 00:00:00 +0000

The var statement#

var declarations, wherever they occur, are processed before any code is executed. This is called hoisting.
The scope of a variable declared with var is its current execution context, which is either the enclosing function or, for variables declared outside any function, global. If you re-declare a JavaScript variable, it will not lose its value.
Assigning a value to an undeclared variable implicitly creates it as a global variable (it becomes a property of the global object) when the assignment is executed.

JS & ES snippet

Mon, 01 Jan 0001 00:00:00 +0000

Setup the global node modules#

Add an environment variable to tell node where the global node module sits

# I use nvm to manage my node and node modules
export NODE_PATH=${HOME}/.nvm/versions/node/<node_version>/lib/node_modules

If you use npm by default, you may have permission problem to access the node modules. I suggest you to set a customized global node module folder under your home directory.
- Create a new folder under your home directory
- Install npm to new global node module
- update environment variables in the profile
```
mkdir $HOME/.node_modules
npm config set prefix $HOME/.node_modules
npm install -g npm
echo 'export NODE_MODULES=$HOME/.node_modules' >> $HOME/.profile
echo 'export PATH=$PATH:$NODE_MODULES/bin' >> $HOME/.profile
source $HOME/.profile
```

Parsing CSV file#

Parse csv file with fast-csv#

Install package fast-csv globally

TS: Basic Types

Mon, 01 Jan 0001 00:00:00 +0000

Basic Types#

In TypeScript, the same types as you would expect in JavaScript are supported, with a convenient enumeration type thrown in to help things along.

Types in JavaScript#

Boolean - The most basic datatype is the simple true/false value, aka boolean value.
```
 let isDone: boolean = false;
```

Number - All numbers in TypeScript are floating point values.

 let decimal: number = 6;
 let hex: number = 0xf00d;
 let binary: number = 0b1010;
 let octal: number = 0o744;

String - Another fundamental part of creating programs in JavaScript for webpages and servers alike is working with textual data. TypeScript also uses double quotes (") or single quotes (’) to surround string data.