


JavaScript date processing function, performance optimization batch processing_Basic knowledge
其实网上写javascript日期格式化的博文很多,大体都看了看,都还不错。唯一遗憾的是只顾着实现了功能,没对函数进行性能优化。
俗话说:不要重复造轮子。google上找了一个比较不错的日期格式化函数,来开始我的优化之旅吧!
google上找的这个日期函数化函数,估计大家都很眼熟,以前我也一直在用。先看看优化后和优化前的效率对比吧!
1、优化之前的toDate函数(字符串转换成Date对象),重复执行1万次,耗时660毫秒
2、优化之前的dateFormat函数(Date对象格式化成字符串),重复执行1万次,耗时676毫秒
3、优化过后的toDate函数,重复执行1万次,耗时122毫秒
4、优化后的dateFormat函数,重复执行1万次,耗时160毫秒
为什么前后差别这么大,其实我也没做多少处理,只是为批处理做了一些缓存而已,认真观察所有网上那些日期格式函数,其实都是用正则进行匹配和替换。其实正则是很耗性能的,于是我在正则匹配的地方做了缓存,把匹配值建立索引。以后就不用每次都去做正则匹配了。
无代码无真相,接下来看看真相吧!
(function(window) { var sinojh = { Version : "1.2", Copyright : "Copyright© sino-jh 2012", Author : "Jeff Lan", Email : "jefflan@live.cn" }; /** * 方便于添加和重写类的属性 * @param {Object} attributes 添加的属性 */ Function.prototype.prototypes = function(attributes) { for ( var a in attributes) { this.prototype[a] = attributes[a]; } }; /** * 获取Url参数 * @param {String} parameter 参数名 * @return {String} 参数值 */ sinojh.getUrlParameter = function(parameter) { if (!sinojh.getUrlParameter.cache) { var url = window.location.href; var paraString = url.substring(url.indexOf("?") + 1, url.length).split("&"); var cache = {}; for ( var i in paraString) { var j = paraString[i]; cache[j.substring(0, j.indexOf("="))] = j.substring(j.indexOf("=") + 1, j.length); } sinojh.getUrlParameter.cache = cache; } return sinojh.getUrlParameter.cache[parameter]; }; /** * 日期格式化 * @param {Date} date 日期对象 * @param {String} formatStyle 格式化样式 * @return {String} 日期型字符串 */ sinojh.dateFormat = function(date, formatStyle) { formatStyle = formatStyle ? formatStyle : sinojh.dateFormat.settings.formatStyle; var time = { "M+" : date.getMonth() + 1, "d+" : date.getDate(), "h+" : date.getHours(), "m+" : date.getMinutes(), "s+" : date.getSeconds(), "S" : date.getMilliseconds() }; if (formatStyle == sinojh.dateFormat.formatStyleCache) { var replaceCache = sinojh.dateFormat.replaceCache; if (replaceCache["y+"]) { formatStyle = formatStyle.replace(replaceCache["y+"].replace, (date.getFullYear() + "").substring(replaceCache["y+"].index)); } for ( var k in time) { if (replaceCache[k]) { formatStyle = formatStyle.replace(replaceCache[k].replace, replaceCache[k].replace.length == 1 ? time[k] : ("00" + time[k]).substring(("" + time[k]).length)); } } } else { sinojh.dateFormat.formatStyleCache = formatStyle; var replaceCache = {}; if (new RegExp("(y+)").test(formatStyle)) { var index = 4 - RegExp.$1.length; replaceCache["y+"] = { replace : RegExp.$1, index : index }; formatStyle = formatStyle.replace(RegExp.$1, (date.getFullYear() + "").substring(index)); } for ( var k in time) { if (new RegExp("(" + k + ")").test(formatStyle)) { replaceCache[k] = { replace : RegExp.$1 }; formatStyle = formatStyle.replace(RegExp.$1, RegExp.$1.length == 1 ? time[k] : ("00" + time[k]).substring(("" + time[k]).length)); } } sinojh.dateFormat.replaceCache = replaceCache; } return formatStyle; }; sinojh.dateFormat.settings = { formatStyle : "yyyy-MM-dd hh:mm:ss" }; /** * 将日期格式的字符串转换成Date对象 * @param {String} dateStr 日期格式字符串 * @param {String} dateStyle 日期格式 * @return {Date} 日期对象 */ sinojh.toDate = function(dateStr, dateStyle) { dateStyle = dateStyle ? dateStyle : sinojh.toDate.settings.dateStyle; var compare = sinojh.toDate.compare; var result = new sinojh.toDate.result(); if (dateStyle == sinojh.toDate.settings.dateStyleCache) { var indexCache = sinojh.toDate.indexCache; for ( var k in compare) { if (indexCache[k]) { result[compare[k]] = dateStr.substring(indexCache[k].index, indexCache[k].index + indexCache[k].length); } } } else { var indexCache = {}; for ( var k in compare) { if (new RegExp("(" + k + ")").test(dateStyle)) { var index = dateStyle.indexOf(RegExp.$1); var length = RegExp.$1.length; indexCache[k] = { index : index, length : length }; result[compare[k]] = dateStr.substring(index, index + length); } } sinojh.toDate.indexCache = indexCache; sinojh.toDate.settings.dateStyleCache = dateStyle; } return new Date(result["y"], result["M"] - 1, result["d"], result["h"], result["m"], result["s"], result["S"]); }; sinojh.toDate.compare = { "y+" : "y", "M+" : "M", "d+" : "d", "h+" : "h", "m+" : "m", "s+" : "s", "S" : "S" }; sinojh.toDate.result = function() { }; sinojh.toDate.result.prototypes( { "y" : "", "M" : "", "d" : "", "h" : "00", "m" : "00", "s" : "00", "S" : "000" }); sinojh.toDate.settings = { dateStyle : "yyyy-MM-dd hh:mm:ss" }; delete Function.prototype.prototypes; window.jh = sinojh; }(this);

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.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

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.


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