Each piece of code is preceded by explanatory text such as functional annotations and parameter requirements. It is not difficult, so no more comments are made. In order to see clearly, here is a small directory in order:
Rewrite window.setTimeout,
Understand the return pattern of recursive programs,
Intercept long strings,
Get the element's position on the page Absolute position,
statistics, removal of duplicate characters (implemented by multiple methods),
random shuffling of ordered array elements (implemented by multiple methods).
/*
Function: Modify window.setTimeout so that it can pass parameters and object parameters (can also be used for setInterval)
Usage method: setTimeout(callback function, time, parameter 1,... ., parameter n) (FF has native support, IE does not support)
*/
var __sto = setTimeout;
window.setTimeout = function(callback,timeout,param){
var args = Array.prototype.slice.call(arguments,2);
var _cb = function(){
callback.apply(null,args);
}
__sto(_cb,timeout);
}
function aaaaa(a,b,c){
alert(a b c);
}
window.setTimeout(aaaaa,2000,5,6,7);
/**//*
Function: Understand the return pattern of recursive programs (from inside to outside)
Mutual references of members between objects
*/
var ninja = {
yell: function(n){
return n > 0 ? ninja.yell(n-1) "a" : "hiy ";
}
};
alert(ninja.yell(4))//The result is: hiyaaaa;
var samurai = { yell: ninja.yell };
//var ninja = {}; // Whether the comment here affects the result
try {
alert(samurai.yell(4));
} catch(e){
alert("Uh , this isn't good! Where'd ninja.yell go?" );
}
/**Function: intercept long string
* @param {string} str String to be intercepted
* @param {number} size interception length (single byte length)
*/
var subStr = function(str, size){
var curSize = 0, arr = [];
for(var i = 0, len = str.length; i arr.push(str.charAt(i)) ;
if (str.charCodeAt(i) > 255){
curSize = 2;
if(size === curSize || size === curSize - 1){
return arr .join('');
}
}else{
curSize ;
if(size === curSize){
return arr.join('');
}
}
}
};
var str = '#%*...What 1234abcd is not long enough';
alert(str.length);
alert( str.substr(0, 15));
alert(subStr(str, 15));
/**//*
Function: Get the absolute position of the element on the page (relative to the upper left corner of the page)
@param {string} node DOM element whose position is to be sought
*/
function getAbsPosition(node) {
var t = node.offsetTop;
var l = node.offsetLeft;
while (node = node.offsetParent) {
t = node.offsetTop;
l = node.offsetLeft;
}
alert("top=" t "n" "left=" l);
}
/**//*
Function: Statistics, removal of repeated characters
@param str String to be counted
Description: Commonly used to count repeated characters in strings, or repeated letters, numbers, etc. in arrays.
Here are two typical types collected from the Internet, each with two implementation methods. There are many other variants, written from different angles, and can be searched and learned.
The data to be counted can be either an array or a string. Just use String.split() or Array.join()
to convert it into the type required by the function parameters.
*/
// Type 1: Use new objects to Save data
var count1 = function (str) {
var map = {}, maxCount = 0, maxChar, undefined, i = str.length;
while (i--) {
var t = str.charAt(i);
map[t] == undefined ? map[t] = 1 : map[t] = 1;
if (map[t] > maxCount) {
maxChar = t;
maxCount = map[maxChar];
}
}
return "Character:" maxChar "Number of times:" maxCount;
}
function s_0(a) { // The parameters here should be array type
var b = {}, c = [], i;
for (i = 0; i if ( !b[a[i]]) {
c[c.length] = a[i], b[a[i]] = true;
}
}
return c;
}
// Type 2: Regular expression matching statistics
var count2 = function (str) {
var most = str.split('').sort().join('') .match(/(.)1*/g); //Arrange repeated characters
most = most.sort(function (a, b) { return a.length - b.length }).pop(); / /Sort by frequency
return most.length ': ' most[0];
}
function s_1(a) {
var a = a.join(""), b = [ ];
while (a.length > 0)
a = a.replace(new RegExp((b[b.length] = a.charAt(0)), "g"), "") ;
return b;
}
/**//*
Function: Disorganize an ordered array (generate an unordered random array)
Description: Basic sorting algorithm Everyone should be very clear. However, the opposite operation is often used in programming, that is, randomly shuffling the original ordered array elements.
The following are three methods. The first one was written by myself before. Due to the poor level, the time complexity of the code I wrote was too high.
So I searched for some simple and efficient methods from the Internet. .
The second is said to be the "shuffling algorithm", which many people must have heard of;
The third is to use the built-in sort method of JS, which is very simple to implement.
*/
// Method 1 (to teach everyone the lessons of failure)
function randArray(num) {
var rands = [];
var ra = parseInt(num * Math .random());
rands.push(ra);
for (var r = 0; r ra = parseInt(num * Math.random() );
for (var m = 0; m while (rands[m] == ra) {
ra = parseInt(num * Math.random() );
m = -1;
}
}
rands.push(ra);
}
//alert(rands);
return rands;
}
//Method 2:
//Select a random number between two [0...array.Length), and exchange the two subscripted elements (this is more efficient in ordering)
/* Note: This is a "shuffling algorithm". Someone has proved that the effect of shuffling is as follows:
The effect of randomly exchanging nums/2 times is very poor. On average, about 1/3 of the objects are still in their original positions
It is basically usable after randomly exchanging nums times, and on average about 15% of the objects are still in the original position
It is really usable after randomly exchanging nums*2 times, and about 2% of the objects are still in the original position on average
*/
function daluan(nums) {
var array=[];
for (var i = 0; i array[i] = i;
}
for (var i = 0; i var rand = parseInt(nums * Math.random());
var temp = array[i];
array[ i] = array[rand];
array[rand] = temp;
}
return array;
}
// Method 3:
// Let the comparison function pass randomly Just return -1 or 1 (the reordering efficiency may not be high)
var testArray3=[1,2,3,4,5,6,7,8,9,10,22,33,55, 77,88,99];
testArray3.sort(function(){return Math.random()>0.5?-1:1;});
alert(testArray3);

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

This article demonstrates frontend integration with a backend secured by Permit, building a functional EdTech SaaS application using Next.js. The frontend fetches user permissions to control UI visibility and ensures API requests adhere to role-base

JavaScript is the core language of modern web development and is widely used for its diversity and flexibility. 1) Front-end development: build dynamic web pages and single-page applications through DOM operations and modern frameworks (such as React, Vue.js, Angular). 2) Server-side development: Node.js uses a non-blocking I/O model to handle high concurrency and real-time applications. 3) Mobile and desktop application development: cross-platform development is realized through ReactNative and Electron to improve development efficiency.

The latest trends in JavaScript include the rise of TypeScript, the popularity of modern frameworks and libraries, and the application of WebAssembly. Future prospects cover more powerful type systems, the development of server-side JavaScript, the expansion of artificial intelligence and machine learning, and the potential of IoT and edge computing.


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