2015-09-28 Seventh Lesson (JS introduction, declaring variables, data types)

vs New Step

FILE--New project--web--blank Web application-Name, location, OK-the software automatically generates a SLN file (solution), and there can be multiple projects under a solution.

Click Project-New Folder CSS and JS and image--new HTML page name Demo1

(Recommended settings: Tools--options--can be set under the font and color; text Editor----to set the number of commonly used languages uplink color hint)

What is JavaScript?

JavaScript is a scripting language, is a scripting language , simple structure , easy to use, its code can be directly placed in HTML documents , can be directly in the support of JavaScript Run in the browser . Javasript makes Web pages more interactive , more lively, and more flexible . When you do something on the Web page, an event occurs , and JavaScript writes a program that responds to the corresponding event .

1, JS Two types of annotation:

1.1. Comments that represent multiple lines : "/* * * *"

For example:

/* Function Myclick () {   alert ("This is my first JS example"); }　　　　*/

1.2, single-line comments: "//"

function Myclick () {//alert ("This is my first JS example"); //}

2, how to use JS:

First specify an event in HTML, and then write JS for this event.

For example: Set a button to name an event on the click button:

<type= "button"  value= "I am a button"  onclick= " ShowMsg () "/>

3, how to write JS:

Write JS can be written in an external JS file, you can also write directly in the head:

<type= "Text/javascript">function  showmsg () {alert (　　　　c7>" This is my first JS example "); }</script>　　

4, naming specification: in order to enhance the readability of the code, so that team members can understand, follow the naming convention.

(1) JS is case-sensitive, very strict.

(2) JS is a weak type, unified with VAR declaration variables, such as:

Shaping: Var inum=10;

Floating point: Var fnum=2.23;

Boolean: Var Bmaie=false;

function: Var fnobject=new myFunction ();

Array: var acolor=new array ();

String: var smystring= "AAAAA";
......

* Weak type and strong type:

JS is a weak type and can only be declared with Var; C # is strongly typed and declared with the corresponding type

Weak type: The way to declare a weakened type; strong type: How to declare a type of emphasis

(3) var can declare multiple variables at the same time:

var girl= "AAAA", age=19, Male=false;

(4) The JS variable does not need to be initialized, can be used later to assign value:

var couple;

(5) Variable name rule:

• The initial letter must be a letter (both uppercase and lowercase), underscore, or dollar sign.

• The remaining letters can be underscores, dollar symbols, any letters or numeric characters.

• Variable names cannot contain JS keywords.

(6) Local variables and global variables:

Global variables: Variables declared outside of {}, each function can be called;

Local variables: Variables declared within {}, only this function is available;

(7) Naming habits

Plastic I:var inum=10;

Floating point F:var fnum=2.23;

Boolean B:var bmaie=false;

function Fn:var fnobject=new myFunction ();

Array A:var acolor=new array ();

String S:var smystring= "AAAAA";

(also: Object o, Regular re, these two are not commonly used, you know)

5. Detailed Data type:

(1) Strings string:

var smystring= "Hello World";

* Supplement: Position/index: The first letter is counted from 0, followed by a space, such as "Hello World" above, the letter of position 8 is R

"Summary of property methods for strings"

Length gets the string length alert (sstring.length); The result is 11.

CharAt gets the character of the specified position, alert (Sstring.charat (8)); The result is R

Intercept alert for substring strings (sstring.substring (1)); Intercept from position 1 to the last. The result is Ello world

Alert (sstring.substring (1,10)); Intercept from position 1 to position 10 (10 not included). The result is Ello Worl

SUBSTR The Intercept alert (SSTRING.SUBSTR (1,6)) of the string; Intercept 6 bits from position 1. The result is Ello W

IndexOf search for a character position alert (Sstring.indexof ("L")); Finds the position where the first L is located, and returns 1 if none. The result is 2.

Alert (Sstring.indexof ("L", 4)); Starting at position 4, find out where the next L is located. The result is 9.

LastindexOf from the back to a character position similar to IndexOf

(2) Boolean type bool: (i.e. True or FALSE, true or false)

Var bmale=true; Declare Bmale to be true;

if (Bmale) {if Bmale is true,

Alert ("a"); then output A;
}

else{otherwise,

Alert ("B"); Then output B.

}

So the above program output a

　　(3) value, and type conversion:

A) The value is added to the string:

var inum1=10;

var snum2= "20";

var snum3=inum1+snum2;

alert (SNUM3);

You can turn INum1 into a string:

var snum3=inum1.tostring () +snum2;

alert (SNUM3);

The sNum2 can also be converted into numerical values:

var inum2=inum1+parseint (sNum2);

alert (INUM2);

b) Add to the floating-point string:

var inum1=10;

var snum2= "20.123";

var snum3=inum1+snum2;

alert (SNUM3);

When the value and the string are added, turn the sNum2 into an integer:

var inum2=inum1+parseint (sNum2);

alert (INUM2);

You can also turn sNum2 into floating-point numbers:

var inum2=inum1+parsefloat (sNum2);

alert (INUM2);

c) Type conversion:

Numeric to String: Var snum1=inum1.tostring ();

String to value: var inum2=parseint (sNum2);

Turn floating point: Var inum2=parsefloat (sNum2);

The string becomes an array: var adate=smystring.split ("-"); (Var smystring= "2015-07-15";)

　　(4) Arrays: storing a data set

A) How the array is declared:

1. Determine the array length: var ateam=new array (12); Array length is 12

2. Indeterminate array Length:

var acolor=new Array ();

Acolor[0]= "Blue";

acolor[1]= "Yellow";

Acolor[2]= "Green";

Acolor[3]= "BLACK";

* The above array can also be written as:

var acolor=new Array ("Blue", "yellow", "green", "Black");

This output: alert (acolor[3]);

Then get: Black

b) toString, the array becomes a string:

Alert (acolor.tostring ());

This time output: Blue,yellow,green,black

c) Join, change the connector:

Alert (Acolor.join ("-"). ToString ());

This time output: Blue-yellow-green-black

d) Split, turn the string into an array:

var smystring= "2015-07-15";

var adate=smystring.split ("-");

Alert (adate[2]);

At this point the output is: 15

e) Reverse the array elements to appear in reverse order:

var acolor=new Array ("Blue", "yellow", "green", "Black");

Alert (Acolor.reverse (). toString ());

At this point the output is: Black,green,yellow,blue

f) Sort, which sorts the array elements according to A-Z order:

var acolor=new Array ("Blue", "yellow", "green", "Black");

Alert (Acolor.sort (). toString ());

At this point the output is: Black,blue,green,yellow

2015-09-28 Seventh Lesson (JS introduction, declaring variables, data types)