Filter, as its name suggests, is to receive an input, process it according to a certain rule, and then return the processed result. It is mainly used for data formatting, such as obtaining a subset of an array, sorting elements in an array, etc. ng has some built-in filters, they are: currency (currency), date (date), filter (substring matching), json (formatted json object), limitTo (limit number), lowercase (lowercase), uppercase (uppercase) ), number (number), orderBy (sort). Nine types in total. In addition, you can also customize filters, which is powerful and can meet any data processing requirements.
AngularJS provides us with some built-in filters. Here are some scenarios for custom filters.
Custom filter without parameters
//过滤 不带参数 app.filter('ordinal', function () { return function (number) { if (isNaN(number) || number < 1) { return number; } else { var lastDigit = number % 10; if (lastDigit === 1) { return number + 'st' } else if (lastDigit === 2) { return number + 'nd' } else if (lastDigit === 3) { return number + 'rd' } else if (lastDigit > 3) { return number + 'th' } } } });
Used roughly like this:
{{777 | ordinal}}
Filtering with parameters
Convert letters in a certain position to uppercase.
//过滤 带参数 app.filter('capitalize', function () { //input 需要过滤的元素 //char位置,索引减一 return function (input, char) { if (isNaN(input)) { //如果序号位置没有设置,索引位置默认是0 var char = char - 1 || 0; //把过滤元素索引位置上的字母转换成大写 var letter = input.charAt(char).toUpperCase(); var out = []; for (var i = 0; i < input.length; i++) { if (i == char) { out.push(letter); } else { out.push(input[i]); } } return out.join(''); } else { return input; } } });
Used roughly like this:
{{'seven' | capitalize:3}}
Filter collection
Filter out the elements in the collection that meet certain conditions.
var app = angular.module('filters', []); app.controller('demo', function ($scope) { $scope.languages = [ {name: 'C#', type: 'static'}, {name: 'PHP', type: 'dynamic'}, {name: 'Go', type: 'static'}, {name: 'JavaScript', type: 'dynamic'}, {name: 'Rust', type: 'static'} ]; }); //过滤集合 app.filter('staticLanguage', function () { return function (input) { var out = []; angular.forEach(input, function (language) { if (language.type === 'static') { out.push(language); } }); return out; } });
Used roughly like this:
<li ng-repeat="lang in languages | staticLanguage">{{lang.name}}</li>
Filter, take multiple parameters, do multiple things
Define the display unit and display position of the number.
var app = angular.module('filters', []); app.controller('demo', function ($scope) { $scope.digit = 29.88; }); //过滤 做多件事 多个参赛 app.filter('customCurrency', function () { return function (input, symbol, place) { if (isNaN(input)) { return input; } else { //检查symbol是否有实参 var symbol = symbol || '¥'; var place = place === undefined ? true : place; if(place===true){ return symbol+input; }else{ return input + symbol; } } } });
Used roughly like this:
<p><strong>Original:</strong></p> <ul><li>{{digit}}</li></ul> <p><strong>Custom Currency Filter</strong></p> <ul> <li>{{digit | customCurrency}} --Default</li> <li>{{digit | customCurrency:'元'}} --custom symbol</li> <li>{{digit | customCurrency:'元':false}} -- custom symbol and custom location</li> </ul>
Two ways to use filter
1. Use filter
in the templateWe can use filter directly in {{}}, followed by | to separate the expression. The syntax is as follows:
{{ expression | filter }}
You can also use multiple filters together. The output of the previous filter will be used as the input of the next filter (no wonder this product looks like a pipe...)
{{ expression | filter1 | filter2 | ... }}
filter can receive parameters, and the parameters are divided by :, as follows:
{{ expression | filter:argument1:argument2:... }}
In addition to formatting the data in {{}}, we can also use filter in the instruction, for example, first filter the array and then loop the output:
<span ng-repeat="a in array | filter ">
2. Use filter in controller and service
Filters can also be used in our js code through the familiar dependency injection. For example, if I want to use the currency filter in a controller, I just need to inject it into the controller. The code is as follows:
app.controller('testC',function($scope,currencyFilter){ $scope.num = currencyFilter(123534); }
Use {{num}} in the template to directly output $123,534.00! The same goes for using filters in services.
At this point you may have doubts. If I want to use multiple filters in the controller, do I have to inject them one by one? Wouldn’t this be too laborious? Little brother, don’t worry~ng provides a $filter service to call the required filter. You only need to inject a $filter. The usage method is as follows:
app.controller('testC',function($scope,$filter){ $scope.num = $filter('currency')(123534); $scope.date = $filter('date')(new Date()); }
The same effect can be achieved. The advantage is that you can use different filters conveniently.

The future trends of Python and JavaScript include: 1. Python will consolidate its position in the fields of scientific computing and AI, 2. JavaScript will promote the development of web technology, 3. Cross-platform development will become a hot topic, and 4. Performance optimization will be the focus. Both will continue to expand application scenarios in their respective fields and make more breakthroughs in performance.

Both Python and JavaScript's choices in development environments are important. 1) Python's development environment includes PyCharm, JupyterNotebook and Anaconda, which are suitable for data science and rapid prototyping. 2) The development environment of JavaScript includes Node.js, VSCode and Webpack, which are suitable for front-end and back-end development. Choosing the right tools according to project needs can improve development efficiency and project success rate.

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.


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