TypeScript basic syntax

First, let’s take a look at the comments. Comments are actually explanations and descriptions of the code. The purpose is to make it easier for people to understand the code. Adding comments to the code is just to improve the readability of the code, and the comments will not be compiled by the computer.

The comment format may be different in different TypeScript . The comments in JavaScript are actually the same as those in 06125c04a0fbb1. Let's take a look.

TypeScript are divided into single-line comments and multi-line comments:

• single-line comment : the following text is the content of the comment.

// 这是一个单行注释

• Multi-line comment : This comment can span multiple lines.

/* 
 这是一个多行注释 
 这是一个多行注释 
 这是一个多行注释 
*/

We will TypeScript code into JavaScript time code, comments will be compiled displayed together. When we run the JavaScript code, the comment code will be ignored and the comment will not be executed.

Example:

For example, add a comment code to the TypeScript

let str :string = "侠课岛";
console.log(str);
// 这是一行注释

Compile and compile it into JavaScript code through tsc test.ts command, the test.js file is as follows:

From the figure, we can see that when TypeScript compiled into JavaScript code, the comment will also be compiled successfully.

TypeScript whitespace and line break

TypeScript language, spaces, tabs and newlines appearing in the program will be ignored. Spaces, tabs, etc. are usually used to indent the code, making the code easy to read and understand.

Example:

In the TypeScript code below, there is a space in the middle of the two lines of code:

let str:string = "你好侠课岛";  

console.log(str);

And after we compiled this code into JavaScript , the space in the middle line is gone:

TypeScript is case sensitive

Students who have studied JavaScript JavaScript is case sensitive. For example, the variable names Age and age are different. That is because TypeScript is a JavaScript , so we can know that TypeScript will also be case sensitive.

Because it is case-sensitive, we must pay special attention to coding variables, function names, etc., to prevent errors.

Example:

For example, we define a variable named xkd , which is named in lowercase letters, and then when we use this variable, we write it as capital letters XKD :

let xkd:string = "侠课岛";  
console.log(XKD);  

An error will be reported when compiling the code in VSCode, as shown below:

As you can see from the above figure, when writing code, the VSCode editor will use a red wavy line to indicate that we are wrong. When the mouse is placed on it, the cause of the error will appear. This is the error message in the VSCode Function.

If you execute the ts file in the terminal, the execution result will also tell us where the error was reported and what was the cause of the error.

Naming conventions

• Use PascalCase (Pascal nomenclature) to name the type.
• Do not use I as the interface name prefix.
• Use PascalCase to name the enumeration value.
• Use camelCase (camel nomenclature) to name the function.
• Use camelCase to name attributes or local variables.
• _ prefix to the private attribute name.
• Use complete word spelling as much as possible.

Pascal nomenclature : PascalCase A method of naming variables in computer programming. Its main feature is to capitalize the first letter of all words that describe the effect of variables, and then connect them directly, without a connector between the words. For example FirstName , LastName , Animal like.

Camel nomenclature : Camel-Case PascalCase , except that Camel-Case just like its name. The first letter of the first word is lowercase, and the first letter of each word after the second word is capitalized. For example firstName , fastName , myFirstName like.

Reserved keywords

TypeScript are shown in the following table:

break	as	catch	switch
case	if	throw	else
var	number	string	get
module	type	instanceof	typeof
public	private	enum	export
finally	for	while	void
null	super	this	new
in	return	true	false
any	extends	static	let
package	implements	interface	function
new	try	yield	const
continue	do

Reserved keywords refer to words that have been defined in high-level languages. We can no longer use these as variable names or function names.

Example:

For example, use the keyword break as the variable name:

let break:string = "关键字";

When the code is executed, the following error message will be output:

The difference between TypeScript and JavaScript

TypeScript can use JavaScript all the code and programming concepts in, TypeScript is to make JavaScript developed and created easier. Here are some differences between TypeScript and JavaScript

• TypeScript requires a clear type, and JavaScript does not require it, because TypeScript is a strongly typed language, and JavaScript is a weakly typed language.
• TypeScript provides static type checking at compile time through type annotations.
• JavaScript TypeScript without any modification. At the same time, a compiler can be used to convert the TypeScript code to JavaScript .
• TypeScript JavaScript object model from the core language aspect and the molding aspect of the class concept.
• TypeScript provides default parameter values.
• TypeScript introduces the concept of "class" that is not in JavaScript
• TypeScript introduces the concept of modules, which can encapsulate declarations, data, functions and classes in modules.

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