Basic javaScript explanation and javascript explanation

Basic javaScript explanation and javascript explanation

The placement of javaScript: <script> and </script> can be placed between head and body, or between body or head.

Six major functions of JavaScript:

1. output directly in script

Document. write ("
2. Respond to the event
<Button type = "button" onclick = "alert ('Welcome! ') "> // Click here </button> // onclick indicates that when a click event is triggered, the alert dialog box appears.
3. Change HTML content
X = document. getElementById ("demo") // search for an element and obtain an element by id. Just as my previous note said that the id can only be used once, so it is unique. X. innerHTML = "Hello JavaScript"; // Changes the content. The value of this element changes when an event is triggered.
4. Change the HTML Image
Element = document. getElementById ('myimage') // obtain the img element. src = "/I/eg_bulboff.gif"; // changing the Src attribute is equivalent to changing an image.
5. Change the HTML Style
X = document. getElementById ("demo") // find the element x. style. color = "# ff0000" by id; // change the style
6. Verification Input
If (isNaN (x) {alert ("Not Numeric")}; // isNaN () is a method used to determine whether all digits in brackets are true.
Three common methods for searching elements in javaScript (excluding jquery)
1: search by id;
X = document. getElementById ("demo") // query by id is unique, and x represents a unique element.
2: search by name:
X = document. getElementsByName ("myInput"); // here, the ments indicates that it returns a set, because the name attribute can be repeatedly defined as X [0]. innerHTML = "Hello JavaScript"; // specify the first few because it is an array. Even if there is only one, it must be written to zero.
3: search by element name:
Var x = document. getElementsByTagName ("input"); // also returns an array alert (x. length); // here there are several input labels to output several JavaScript comments, which are the same as those in java. // and /**/
JavaScript Variables
JavaScript data includes strings, numbers, Boolean values, arrays, objects, Null values, and Undefined values.
Var cars = new Array (); cars [0] = "Audi"; // Array expression var cars = ["Audi", "BMW", "Volvo"]; // It is also an array expression person = new Object (); // Object expression
JavaScript Functions
Function getElements () {}// if you can include a parameter, pass the parameter (var1, var2) to it. If you want to return a return value, the function type remains unchanged.
JavaScript operators, Arithmetic Operators, value assignment operators, comparison operators, logical operators, conditional operators, IF statements, Switch statements, For loops, while do-while, break and Continue are the same as java rules (a little different is for (x in person ))
Next we will make a few small cases:
1: the account name is verified, and the two passwords are consistent.
<% @ Page language = "java" import = "java. util. *" pageEncoding = "UTF-8" %> <! Doctype html> 
The running result is as follows:

2: Implement an addition Calculator
<% @ Page language = "java" import = "java. util. *" pageEncoding = "UTF-8" %> <! Doctype html> 
The running result is as follows:

The above is all the content of this article. I hope this article will help you in your study or work. I also hope to provide more support to the customer's home!