1. Creating an array
just declares the array and does not contain specific data.
Java code
var checkboxlist = new array();
Create an array and specify the length. This length of 5 can be changed and can grow automatically.
Java code
var checkboxlist = new array(5);
Create an array and initialize three elements.
Java code
var checkboxlist = new array("1111", "2222", "3333");
2. Array operation
2.1 push() Add an element to the end of the array and return the latest length of the array
Change the string "userid001 "Put it at the end of the array
Java code
checkboxlist.push("userid001");
Add two elements at a time, "aaaa" and "bbbb"
Java code
checkboxlist.push("aaaa", "bbbb");
2.2 unshift() Insert elements at the beginning of the array, and move the original elements backward
Insert two elements at the beginning of the array.
(Some information says that the return value is the latest length of the array, but I tested the return value in ie6 to be "undefined")
Java code
checkboxlist.unshift("aaaa","bbbb");
2.3 pop() removes the end of the array an element and returns that element.
Code:
Java code
checkboxlist.pop();
2.3 shift() removes an element at the beginning of the array and returns the element
Code:
Java code
checkboxlist.shift()
2.4 splice() insert ( Replace) or remove multiple elements
Example of removal:
splice(delindex,delcount);
delindex: The position to start removing, which is the subscript of the array, starting from 0.
delcount: The number of elements removed.
Start from the first element of the array and remove 2 elements.
Java code
checkboxlist.splice(0,2);
For example: after executing checkboxlist.splice(1,2), the array changed from the original 4 elements to only "1111" and "4444" element.
Java code
var checkboxlist = new array();checkboxlist.push("1111");checkboxlist.push("2222");checkboxlist.push("3333");checkboxlist.push("4444");// Starting from the second element of the array, remove 2 elements. checkboxlist.splice(1,2);alert(checkboxlist);
Insertion (replacement) example:
splice(addindex,replacecount,elememt...);
addindex: insert (replace) starting position, which is the array Subscript, starting from 0.
replacecount: The number of elements that need to be replaced.
elememt...: New element, which can be one or more.
When replacecount is less than or equal to 0, only add.
For example: insert two elements "aaaa" and "bbbb" after the first element ("1111") of the checkboxlist array.
Java code
var checkboxlist = new array("1111","2222","3333","4444","5555");checkboxlist.splice(1,0,"aaaa","bbbb");alert( checkboxlist);
When replacecount is greater than 0, the element will be replaced.
For example: replace the element (that is, "2222") after the first element ("1111") of the checkboxlist array with "aaaa", "bbbb". The latest value of checkboxlist in the code below is: "1111", "aaaa", "bbbb", "3333", "4444", "5555"
Java code
var checkboxlist = new array("1111", "2222", "3333","4444","5555");checkboxlist.splice(1,1,"aaaa","bbbb");alert(checkboxlist);
If the value of the replacecount parameter is greater than the length of the array, it will Replace all elements starting with the addindex parameter. After execution, the elements of the checkboxlist become: "1111", "aaaa", "bbbb"
Java code
var checkboxlist = new array("1111", "2222", "3333", "4444", "5555") ;checkboxlist.splice(1,9,"aaaa","bbbb");alert(checkboxlist);
2.5 reverse() Reverse the order of array elements
Java code
checkboxlist.reverse();
2.6 sort() Sort array elements in natural order
Java code
checkboxlist.sort();
2.7 concat() copies another array, generates a new array, and returns the elements in
alllist as a collection of elements in checkboxlist and radiolist
Java code
var checkboxlist = new array("1111","2222");var radiolist = new array("aaaa","bbbb");var alllist = checkboxlist.concat(radiolist);
2.8 slice() copy Specify the element after the serial number, generate a new array, and return
slice(index)
index: copy starting position, which is the subscript of the array, starting from 0.
When the index is greater than the number of array elements, an empty array is returned.
Copy all elements after the first element of the checkboxlist to the new temparray array, and the original checkboxlist will not change.
Java code
var checkboxlist = new array("1111","2222","3333");var temparray = checkboxlist.slice(1);
2.9 join() string operation
join(separator);
separator: The added separator can be "" empty string.
Can perform efficient string addition. Much more efficient than direct string addition.
Code example:
Java code
var checkboxlist = new array("1111","2222","3333","4444");var strdata = checkboxlist.join("|");alert(strdata);
2.10 length attribute
length returns the length of the array, which is the number of elements.
Java code
var checkboxlist = new array("1111","2222","3333","4444");alert(checkboxlist.length);

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

C and JavaScript achieve interoperability through WebAssembly. 1) C code is compiled into WebAssembly module and introduced into JavaScript environment to enhance computing power. 2) In game development, C handles physics engines and graphics rendering, and JavaScript is responsible for game logic and user interface.

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.


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