implementation of 1.JSThe JS script must be located between the <script> and </script> tags the script tag can be placed in the head or body tag of the HTML file. Generally I like to put it in the head. A. Put it in the head, for example
<body> <p id= "Demo" > A Paragraph </p>
<button type= "button" onclick= "MyFunction ()" > click here </button>
</body>
<body> <p id= "Demo" > A Paragraph </p>
<button type= "button" onclick= "MyFunction ()" > click here </button>
The <!-script is placed on the last side of the body-> <script> function MyFunction () {document.getElementById ("demo"). Inn Erhtml= "My I-JavaScript Function"; } </script>
</body>
function MyFunction () {document.getElementById ("demo"). Innerhtml= "My I-JavaScript Function";}
Here to introduce the external JS file:
<body> <p id= "Demo" > A Paragraph </p>
<button type= "button" onclick= "MyFunction ()" > click here </button> </body>
Note: Whether externally or directly embedded in HTML, each script tag is publicly accessible to each other in the code, so multiple script tags can be synthesized into a script tag pair. External scripts cannot contain <script> tags.
output of 2.JSA. Manipulating HTML elements: using ID attributes to mark HTML elements, and then using IDs to access the elements such as: <body> <p id= "Demo" > My Paragraph. </p> </body>
B. Writing information to HTML documents <body> Note: If you execute document.write after the document has finished loading, the entire HTML page will be overwritten:
3. NoteThe comments in the JS code use://This is a single-line comment or/** this is a multiline comment/html comment used: <!-html comments >
variables in the 4.JSBecause JS is a weak data type language, declaring variables using the var keyword can be. var carname= "Volvo";
var name= "Gates", age=56, job= "CEO"; Note: If a variable is declared but not assigned, the value of the variable is undefined, the variable can be declared repeatedly, and if it is not assigned again when it is declared, it will not change its value. If we assign a value to a variable that does not use the keyword VAR declaration, then the variable becomes a global variable.
data types in 5.JSnumeric type, var x = 6; If the prefix is 0, JavaScript interprets numeric constants as octal numbers, and if the prefix is 0 and "X", it is interpreted as a hexadecimal number. var y=0377; var Z=0xff; Some common attributes of your property constants and methods,
Properties:MAX value MIN value NEGATIVE infinitive POSITIVE infinitive NaN prototype constructor
Method:Toexponential () toFixed () toprecision () toString () valueof ()
String type,
var carname= "Bill Gates";
var carname= ' Bill Gates ';
String Object Properties
| Property |
Description |
| Constructor |
A reference to the function that created the object |
| Length |
Length of string |
| Prototype |
Allows you to add properties and methods to an object |
String Object method
The
| method |
Description |
| anchor () |
creates an HTML anchor. |
| big () |
displays a string in a large font. The |
| Blink () |
displays a flashing string. The |
| Bold () |
displays the string in bold. The |
| charAt () |
returns the character at the specified position. The |
| charcodeat () |
returns the Unicode encoding of the character at the specified location. |
| concat () |
connection string. The |
| fixed () |
displays the string in typewriter text. The |
| fontcolor () |
uses the specified color to display the string. The |
| fontsize () |
uses the specified dimensions to display the string. The |
| fromcharcode () |
creates a string from a character encoding. The |
| indexOf () |
retrieves the string. The |
| italics () |
uses italics to display a string. The |
| lastindexof () |
searches the string forward from behind. |
| link () |
