Basic syntax for JavaScript

1, the basic structure of the script is as follows:

<script language= "JavaScript" >          <!--javascript statements;-->       

Tip: You typically place core script statements between tags

The document.write () method is used for page output display information.

Question: Why does the browser display the contents of the script rather than the results of the script execution?
A, omission start or end of <script>. b, the extension is not. html or. htm. C, the browser does not support JS script.

2, the principle of implementation:
Client requests a page with JavaScript

　　Download pages with javascript from the server side　　

Client-side parsing of HTML tags and JavaScript scripts

3. Basic syntax:
var a valid variable name;
Variable names cannot use keywords. Multiple variables can be separated by commas.

The operation symbol is the same as in Java

if (expression) {}else{}

for (initialize; condition; increment or decrement) {}

while (condition) {}

switch (expression)
{Case constant value 1:javascript statement;

Case constant Value 2:javascript statement;

Default:javascript statement;

}
Type: Number/null/boolean/string/object/undefinde

Type conversions: Mastering the Parsefloat () and parseint () functions.

Focus on defining functions: Function function name (argument list) {}

Note: You can also have no parameters
Call Function: Event name = "function name ()"
Get form data: document. Table sole name. form element name. value

Example 1:function Calcu () {
var Numb1=document.calc.num1.value;

var Numb2=document.calc.num2.value;

var total=parsefloat (NUMB1) *parsefloat (NUMB2);

Document.calc.result.value=total; }        

<form name= "Calc" >

<input name= "Result" type= "text" size= ">"
<input name= "getanswer" type= "button" id= "Getanswer" onclick= "CALCU ()" >

</form>

Example 2: Print the inverted pyramid line

var i = 25;

while (i>0) {
Docment.write ("

i=i-5;

}
for (Var j=5;j<30;j=j+5) {
Docment.write ("When defining functions, note:
Formal parameters: The parameters defined for a function when the function is defined, which represents the type and location of the parameter.

Actual parameter: The parameter value passed to the function when the function is called.

When called: passes the value of the argument to the parameter.

Function names are strictly case-sensitive.

Multiple parameters are separated by commas, and you must specify a type-compatible value for each parameter separated by commas when you want to invoke the function.

If you need to return a result, use the return statement.

Basic syntax for JavaScript