The main feature of AngularJS is that it allows us to extend the functionality of HTML to serve the purpose of today’s dynamic web pages. In this article, I'll show you how to use AngularJS's directives to make your development faster and easier, and make your code more maintainable.
Prepare
Step 1: HTML Template
To make things easier, we will write all the code in one HTML file. Create it and put a basic HTML template into it:
<!DOCTYPE html> <html> <head> </head> <body> </body> </html>
Now add the angular.min.js file from Google CDN to <head> of the document:
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.min.js"></script>
Step 2: Create module
Now let's create the module for the directive. I'll call it example, but you can choose any name you want, just remember that we will use this name as the namespace for the directive we create later.
Put this code in a script tag at the bottom of <head>:
var module = angular.module('example', []);
We don't have any dependencies, so the array in the second parameter of angular.module() is empty, but don't remove it completely or you will get the $injector:nomod error because # The single-argument form of ##angular.module() retrieves a reference to an existing module instead of creating a new module.
ng-app="example" attribute to the <body> tag for the application to work properly. The file should then look like this:
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.min.js"></script> <script> var module = angular.module('example', []); </script>
</head>
<body ng-app="example">
</body>
</html>
Attribute command: 1337 C0NV3R73R
First, we will create a simple directive that will work similarly to ngBind, but it will change the text to leet talk.
Step 1: Instruction Statement
Usemodule.directive() method to declare instructions:
module.directive('exampleBindLeet', function () {
The first parameter is the name of the instruction. It must be in camelCase, but since HTML is not case-sensitive, you will use dash-delimited lowercase (example-bind-leet) in the HTML code. The function passed as the second parameter must return an object describing the instruction. Currently it has only one attribute: link function:
return {
link: link
};
});
Step 2: Link function
You can define the function before the return statement or directly in the returned object. It is used to manipulate the DOM of the element our directive applies to, and is called with three arguments:
function link($scope, $elem, attrs) {
$scope is an Angular scope object, $elem is the DOM element matched by this directive (it is wrapped in jqLite??e, which is jQuery for AngularJS A subset of the most commonly used functions) attrs is an object with all the element attributes (with canonicalized names, so example-bind-leet will be available as attrs.exampleBindLeet).
var leetText = attrs.exampleBindLeet.replace(/[abegilostz]/gmi, function (letter) {
return leet[letter.toLowerCase()];
});
$elem.text(leetText);
}
First, we replace some letters in the text provided in the example-bind-leet attribute with the replacement content from the leet table. The table looks like this:
var leet = {
a: '4', b: '8', e: '3',
g: '6', i: '!', l: '1',
o: '0', s: '5', t: '7',
z: '2'
};
You should put it on top of the <script> tag. As you can see, this is the most basic leet converter since it only replaces ten characters.
text() method to put into the inner text of the element matched by this directive.
<body> of your document:
<div example-bind-leet="This text will be converted to leet speak!"></div>The output should look like this:
But that's not exactly how the
ngBind directive works. We'll change this in the next steps.
Step 3: Scope
First of all, what is passed in theexample-bind-leet attribute should be a reference to the variable in the current scope, not the text we want to convert. To do this, we must create an isolated scope for the directive.
module.directive('exampleBindLeet', function () {
...
return {
link: link,
scope: {
}
};
);
Every property in this object will be available within the scope of the directive. Its value will be determined by the value here. If we use "-" then the value will be equal to the value of the property with the same name. Using "=" will tell the compiler that we expect to pass variables in the current scope - this will work like ngBind:
scope: {
exampleBindLeet: '='
}
You can also use anything as a property name and put the normalized (converted to camelCase) property name after - or =:
scope: {
text: '=exampleBindLeet'
}
Choose the one that suits you best. Now we also have to change the link function to use $scope instead of attr:
function link($scope, $elem, attrs) {
var leetText = $scope.exampleBindLeet.replace(/[abegilostz]/gmi, function (letter) {
return leet[letter.toLowerCase()];
});
$elem.text(leetText);
}
現(xiàn)在使用 ngInit 或創(chuàng)建一個(gè)控制器，并將 div 的 example-bind-leet 屬性的值更改為您使用的變量的名稱：
<body ng-app="example" ng-init="textToConvert = 'This text will be converted to leet speak!'">
<div example-bind-leet="textToConvert"></div>
</body>
第 4 步：檢測更改
但這仍然不是 ngBind 的工作原理。要查看我們添加一個(gè)輸入字段以在頁面加載后更改 textToConvert 的值：
<input ng-model="textToConvert">
現(xiàn)在，如果您打開頁面并嘗試更改輸入中的文本，您將看到我們的 div 中沒有任何變化。這是因?yàn)?link() 函數(shù)在編譯時(shí)每個(gè)指令都會調(diào)用一次，因此它無法在每次范圍內(nèi)發(fā)生更改時(shí)更改元素的內(nèi)容。
要改變這一點(diǎn)，我們將使用 $scope.$watch() 方法。它接受兩個(gè)參數(shù)：第一個(gè)是 Angular 表達(dá)式，每次修改范圍時(shí)都會對其進(jìn)行求值，第二個(gè)是回調(diào)函數(shù)，當(dāng)表達(dá)式的值發(fā)生更改時(shí)將被調(diào)用。
首先，讓我們將 link() 函數(shù)中的代碼放入其中的本地函數(shù)中：
function link($scope, $elem, attrs) {
function convertText() {
var leetText = $scope.exampleBindLeet.replace(/[abegilostz]/gmi, function (letter) {
return leet[letter.toLowerCase()];
});
$elem.text(leetText);
}
}
現(xiàn)在，在該函數(shù)之后，我們將調(diào)用 $scope.$watch()，如下所示：
$scope.$watch('exampleBindLeet', convertLeet);
如果您現(xiàn)在打開頁面并更改輸入字段中的某些內(nèi)容，您將看到 div 的內(nèi)容也按預(yù)期發(fā)生了變化。
元素指令：進(jìn)度條
現(xiàn)在我們將編寫一個(gè)指令來為我們創(chuàng)建一個(gè)進(jìn)度條。為此，我們將使用一個(gè)新元素：<example-progress>。
第 1 步：樣式
為了讓我們的進(jìn)度條看起來像一個(gè)進(jìn)度條，我們必須使用一些 CSS。將此代碼放入文檔的 <head> 中的 <style> 元素中：
example-progress {
display: block;
width: 100%;
position: relative;
border: 1px solid black;
height: 18px;
}
example-progress .progressBar {
position: absolute;
top: 0;
left: 0;
bottom: 0;
background: green;
}
example-progress .progressValue {
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
text-align: center;
}
正如你所看到的，它非?；?- 我們使用 position:relative 和 position:absolute 的組合來定位綠色條和 <example-progress> 元素。
第 2 步：指令的屬性
與前一個(gè)相比，這個(gè)需要更多的選項(xiàng)?？匆幌逻@段代碼（并將其插入到您的 <script> 標(biāo)記中）：
module.directive('exampleProgress', function () {
return {
restrict: 'E',
scope: {
value: '=',
max: '='
},
template: '',
link: link
};
});
正如您所看到的，我們?nèi)匀皇褂梅秶ㄟ@次有兩個(gè)屬性 - value 表示當(dāng)前值，max 表示最大值）和 link() 函數(shù)，但有兩個(gè)新屬性：
- restrict: 'E' - 這告訴編譯器查找元素而不是屬性?？赡艿闹禐椋?/li>
- 'A' - 僅匹配屬性名稱（這是默認(rèn)行為，因此如果您只想匹配屬性，則無需設(shè)置它）
- 'E' - 僅匹配元素名稱
- 'C' - 僅匹配類名
- 您可以將它們組合起來，例如“AEC”將匹配屬性、元素和類名稱。
- template: '' - 這允許我們更改元素的內(nèi)部 HTML（如果您想從單獨(dú)的文件加載 HTML，還有 templateUrl）
當(dāng)然，我們不會將模板留空。將此 HTML 放在那里：
<div class="progressBar"></div><div class="progressValue">{{ percentValue }}%</div>
如您所見，我們還可以在模板中使用 Angluar 表達(dá)式 - percentValue 將從指令的范圍中獲取。
第3步：鏈接函數(shù)
該函數(shù)與上一個(gè)指令中的函數(shù)類似。首先，創(chuàng)建一個(gè)將執(zhí)行指令邏輯的本地函數(shù) - 在本例中更新 percentValue 并設(shè)置 div.progressBar 的寬度：
function link($scope, $elem, attrs) {
function updateProgress() {
var percentValue = Math.round($scope.value / $scope.max * 100);
$scope.percentValue = Math.min(Math.max(percentValue, 0), 100);
$elem.children()[0].style.width = $scope.percentValue + '%';
}
}
正如你所看到的，我們不能使用 .css() 來更改 div.progressBar 的寬度，因?yàn)?jqLit??e 不支持 .children( )。我們還需要使用 Math.min() 和 Math.max() 將值保持在 0% 到 100% 之間 - 如果 precentValue 小于 0，則 Math.max() 將返回 0；如果 percentValue 大于 100，則 Math.min() 將返回 100。
現(xiàn)在不再是兩個(gè) $scope.$watch() 調(diào)用（我們必須注意 $scope.value 和 中的變化$scope.max) 讓我們使用 $scope.$watchCollection()，它類似，但適用于屬性集合：
$scope.$watchCollection('[value, max]', updateProgress);
請注意，我們傳遞的第一個(gè)參數(shù)看起來像數(shù)組，而不是 JavaScript 的數(shù)組。
要了解它是如何工作的，首先更改 ngInit 以初始化另外兩個(gè)變量：
<body ng-app="example" ng-init="textToConvert = 'This text will be converted to leet speak!'; progressValue = 20; progressMax = 100">
然后在我們之前使用的 div 下面添加 <example-progress> 元素：
<example-progress value="progressValue" max="progressMax"></example-progress>
<body> 現(xiàn)在應(yīng)該如下所示：
<body ng-app="example" ng-init="textToConvert = 'This text will be converted to leet speak!'; progressValue = 20; progressMax = 100">
<div example-bind-leet="textToConvert"></div>
<example-progress value="progressValue" max="progressMax"></example-progress>
</body>
這就是結(jié)果：
第 4 步：使用 jQuery 添加動畫
如果您為 progressValue 和 progressMax 添加輸入，如下所示：
<input ng-model="progressValue"> <input ng-model="progressMax">
您會注意到，當(dāng)您更改任何值時(shí)，寬度會立即發(fā)生變化。為了讓它看起來更好一點(diǎn)，讓我們使用 jQuery 來制作它的動畫。將 jQuery 與 AngularJS 結(jié)合使用的好處是，當(dāng)您包含 jQuery 的 <script> 時(shí)，Angular 會自動用它替換 jqLit??e，使 $elem 成為 jQuery 對象。
因此，讓我們首先將 jQuery 腳本添加到文檔的 <head> 中，位于 AngularJS 之前：
<script src="http://code.jquery.com/jquery-2.1.0.min.js"></script>
現(xiàn)在我們可以更改 updateProgress() 函數(shù)以使用 jQuery 的 .animate() 方法。更改此行：
$elem.children()[0].style.width = $scope.percentValue + '%';
對此：
$elem.children('.progressBar').stop(true, true).animate({ width: $scope.percentValue + '%' });
并且您應(yīng)該有一個(gè)精美的動畫進(jìn)度條。我們必須使用 .stop() 方法來停止并完成任何待處理的動畫，以防我們在動畫進(jìn)行過程中更改任何值（嘗試刪除它并快速更改輸入中的值以了解為什么需要它）。 p>
當(dāng)然，您應(yīng)該更改 CSS，并可能在應(yīng)用程序中使用其他一些緩動函數(shù)來匹配您的風(fēng)格。
結(jié)論
AngularJS 的指令對于任何 Web 開發(fā)人員來說都是一個(gè)強(qiáng)大的工具。您可以創(chuàng)建一組自己的指令來簡化和促進(jìn)您的開發(fā)過程。您可以創(chuàng)建的內(nèi)容僅受您的想象力限制，您幾乎可以將所有服務(wù)器端模板轉(zhuǎn)換為 AngularJS 指令。
有用鏈接
以下是 AngularJS 文檔的一些鏈接：
- 開發(fā)者指南：指令
- 綜合指令 API
- jqLit??e（angular.element）API
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