JavaScript Basics (iii)

Data type

1. String

2. Numerical type

3. Boolean type

4. Objects

5. Arrays

In order to be more standard, make oneself in the future work more easy and convenient maintenance, adopt some data type of name life habit

Type	Prefix	Example
Array	A	Aarray
Boolean value	B	Bmale
Floating point	F	FTax
Function	Fn	Fnswap
Integral type	I	Iage
Object	O	Ocar
Regular	Re	Repattern
String	S	Suniversity

A string of strings

var smystring = "Hello World";

The string can be any text in quotation marks. You can use single and double quotation marks.

Instance:

Code: var smystring = "Hello World"; var smystring = ' Hello World '; var smystring = ' Hello World '; var smystring = "' Hello World '"; Result: Hello Worldhello World "Hello World"

The string has the length property and can return the number of strings in the variable.

var smystring = "Hello World";  document.write (smystring.length); // number of strings for output smystring: One

Gets the character at the specified position, which can be used with the charAt () function.

Note: The first character position is 0, the second character is 1, and so on.

var smystring = "Hello World";  document.write (Smystring.charat (1)); // the output is: E

If you want to get a string from a variable, you can use substring () or substr ()

var smystring = "ABCDEFG"  document.write (smystring.substring (// output BCDEFG, Intercept from position 1 to last  // output BCD, intercept from position 1 to position 4, not including position 4

var smystring = "ABCDEFG"  // output BCDE, starting from position 1, intercept 4-bit

On the search string, you can use IndexOf () or lastindexOf (),

IndexOf (): Returns the index value in the source string for the first occurrence of a substring within the source string, is an integer, and the lookup direction is left to right

LastindexOf (): The lookup direction is from right to left,

Returns 1 if no substring is found

var smystring = "Abcdefghijk"= Smystring.indexof ("E") + "<br>";  // find the location of E from the Go // Optional parameters, looking backwards from the first few characters s3 = Smystring.lastindexof ("E") + "<br>";  // find from the back forward // Optional parameters, looking forward from the first few characters document.write (S1);d ocument.write (S2);d ocument.write (S3);d Ocument.write (S4);

Results:

444-1

Second, BOOL Boolean

Selectable values: True, Fasle

  copy code copy code  var  bb = false ; //  declares that BB is false  if  (BB) {//  document.write ("AAA"  + "<br>"); //  just output AAA    else  {/ /  otherwise  document.write ("CCC" + "<br>"); //     result output: CCC   copy code copy code  

() to display the type of the variable: var true ;      document.write (typeof (BB) + "<br>"); var false ;d ocument.write (typeof (BB) + "<br>"); var bb = "12345";d ocument.write (typeof (BB) + "<br>"); var bb = 12345;d ocument.write (typeof (BB) + "<br>");

Results:

Boolean Boolean Stringnumber

Third, numeric number

In JavaScript, you want to limit the value of a number without qualifying it as an integer or floating-point type

  var iNum1 = ten;   var fNum2 = 56.41;   var iNum3 = -41;  document.write (iNum1+ "+inum2+" "+iNum3); // output Result: ten 56.41-41

Iv. Types of conversions

ToString (): Converts a logical value to a string and returns the result.

varA = 3;varb = A + 3;varc = "Student" +A;varD =a.tostring ();varE = a + "";d Ocument.write (a+ "+ B +" "+ C +" "+ D +" "+ e+" <br> ");d Ocument.write (typeof(a) + "" +typeof(b) + "" +typeof(c) + "" +typeof(d) + "" +typeof(e));//Output Result:3 6 Student3 3 3 Number Number string string

parseint (): Converts a string to an integer.

Parsefloat (): Converts a string into a floating-point type.

Only characters can call these two methods, otherwise they are converted to Nan. At the time of conversion, the character at position 0 is checked first, and if the character is a valid character, the character at 1 is checked, and if it is not a valid character, the conversion is just terminated.

Document.writeln (parseint ("4555.5544") + "<br>");d Ocument.writeln (parseint ("0.5544") + "<br>" );d Ocument.writeln (parseint ("a0.5544") + "<br>");d Ocument.writeln (parsefloat ("4555.5544") ) + "<br>");d Ocument.writeln (parsefloat ("3a.5544") + "<br>");d Ocument.writeln (parsefloat ( "a0.5544") + "<br>");

Results:

45550nan4555.55443nan

V. Array of arrays

An array is a set of variables that have the same type and name. These variables are called array elements (element), each array element has a number, this number is called subscript, we can use subscript to distinguish these elements. The number of array elements is also known as the length of the array.

In JavaScript, arrays are created using the keyword array declaration, and you can also declare the length of a variable.

Cases:
var amyarray = new Array (9); Declaring the length of a variable

When you are unsure of the final number of arrays, you can declare an array without specifying a specific number.

Example: var New //  amyarray[0] = 1234; amyarray[1] = "1234"; amyarray[2] = "Red"; amyarray[3] = "Blue" 
   
    ; amyarray[4] = "BLACK"
    
    // 
    output to page
   

output effect:1234,1234,red,blue,black

Alternatively, you can create an array directly

Example: var New Array (1234, "1234", "Red", "Blue", "Black");d ocument.write (Amyarray+ "<br>");d Ocument.write (  typeof(amyarray[0]) + "" +typeof// output array element data type

output effect:1234,1234, red,blue,blacknumber string

In addition, you can also use

Arrays can be converted to strings using toString ()

var amyarray = new Array (1234, "1234", "Red", "Blue", "Black");d Ocument.write (amyarray.tostring () + "<br>");

Join () changes the connector between arrays

Example:var amyarray = new Array (1234, "1234", "Red", "Blue", "Black");d Ocument.write (amyarray.tostring () + "<br& gt; "); document.write (Amyarray.join ("-"). ToString () + "<br>");d Ocument.write (Amyarray.join ("+")); Effect:1234,1234,red,blue,black1234-1234-red-blue-black1234+1234+red+blue+black

Split () turns the string into an array

Example:var smystring = ("1234,red,blue,black"), var Amyarray = Smystring.split (",");d Ocument.write (smystring+ " <br> ");d Ocument.write (Amyarray.join ("-")); Effect:1234,red,blue,black1234-red-blue-black

Reverse () reverse the array elements

Example: var smystring = ("1234,red,blue,black"); var amyarray = Smystring.split (",");d ocument.write (smystring+ "<br>");d Ocument.write ( Amyarray.join ("-") + "<br>");d Ocument.write (Amyarray.reverse (). Join ("+")); Effect:1234 , Red,blue,black1234-red-blue-blackblack+blue+red+1234

Use sort () to sort the elements of an array in alphabetical order

Example: var smystring = ("1234,red,blue,black"); var amyarray = Smystring.split (",");d ocument.write (smystring+ "<br>");d Ocument.write ( Amyarray.join ("-") + "<br>");d Ocument.write (Amyarray.reverse (). Join ("+") + "<br>"); document.write (Amyarray.sort (). Join ("=")); Effect:1234, red,blue,black1234-red-blue-  Blackblack+blue+red+12341234=black=blue=red

JavaScript Basics (iii)