Detailed introduction to the application scenarios and implementation principles of JavaScript template engine-JS Tutorial-php.cn

Detailed introduction to the application scenarios and implementation principles of JavaScript template engine

黄舟

Release： 2017-03-16 14:58:28

Original

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一、应用场景

以下应用场景可以使用模板引擎：
1、如果你有动态ajax请求数据并需要封装成视图展现给用户，想要提高自己的工作效率。
2、如果你是拼串族或者数组push族，迫切的希望改变现有的书写方式。
3、如果你在页面布局中，存在共性模块和布局，你可以提取出公共模板，减少维护的数量。

二、实现原理

不同模板间实现原理大同小异，各有优缺，请按需选择，以下示例以artTemplate模板引擎来分析。

2.1 模板存放

模板一般都是放置到textarea/input等表单控件，或者script[type="text/html"]等标签中，如下：

<script id="test" type="text/html">
	{{if isAdmin}}

	<h1>{{title}}</h1>
	<ul>
	    {{each user as name i}}
	        <li> {{i + 1}} ：{{name}}</li>
	    {{/each}}
	</ul>

	{{/if}}
</script>

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//textarea或input则取value，其它情况取innerHTML

2.2 模板函数

一般都是templateFun(“id”, data);其中id为存放模板字符串的元素id，data为需要装载的数据。

2.3 模板获取

一般都是通过ID来获取，document.getElementById(“ID”):

//textarea或input则取value，其它情况取innerHTML
var html = /^(textarea|input)$/i.test(element.nodeName) ? element.value : element.innerHTML;

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2.4 模板解析——处理html语句和逻辑语句及其他格式化处理

这步的主要操作其实多余的空格，解析出html元素和逻辑语句及关键字。例如：artTemplate.js中的代码实现：

defaults.parser = function (code, options) {
    // var match = code.match(/([\w\$]*)(\b.*)/);
    // var key = match[1];
    // var args = match[2];
    // var split = args.split(&#39; &#39;);
    // split.shift();

    //if isAdmin
    code = code.replace(/^\s/, &#39;&#39;);

    //["if", "isAdmin"]
    var split = code.split(&#39; &#39;);
    //if
    var key = split.shift();
    //isAdmin
    var args = split.join(&#39; &#39;);

    switch (key) {

        case &#39;if&#39;:
            //if(isAdmin){
            code = &#39;if(&#39; + args + &#39;){&#39;;
            break;

        case &#39;else&#39;:

            if (split.shift() === &#39;if&#39;) {
                split = &#39; if(&#39; + split.join(&#39; &#39;) + &#39;)&#39;;
            } else {
                split = &#39;&#39;;
            }

            code = &#39;}else&#39; + split + &#39;{&#39;;
            break;

        case &#39;/if&#39;:

            code = &#39;}&#39;;
            break;

        case &#39;each&#39;:

            var object = split[0] || &#39;$data&#39;;
            var as     = split[1] || &#39;as&#39;;
            var value  = split[2] || &#39;$value&#39;;
            var index  = split[3] || &#39;$index&#39;;

            var param   = value + &#39;,&#39; + index;

            if (as !== &#39;as&#39;) {
                object = &#39;[]&#39;;
            }

            code =  &#39;$each(&#39; + object + &#39;,function(&#39; + param + &#39;){&#39;;
            break;

        case &#39;/each&#39;:

            code = &#39;});&#39;;
            break;

        case &#39;echo&#39;:

            code = &#39;print(&#39; + args + &#39;);&#39;;
            break;

        case &#39;print&#39;:
        case &#39;include&#39;:

            code = key + &#39;(&#39; + split.join(&#39;,&#39;) + &#39;);&#39;;
            break;

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例如上例中：”{{if isAdmin}}”最终被解析成”if(isAdmin){”，”{{/if}}“被解析成“}”。

2.5 模板编译——字符串拼接成生成函数的过程

这步的主要操作就是字符串的拼接成生成函数，看看artTemplate的部分源码：

function compiler (source, options) {
    /*
    openTag: &#39;<%&#39;,    // 逻辑语法开始标签
    closeTag: &#39;%>&#39;,   // 逻辑语法结束标签
    escape: true,     // 是否编码输出变量的 HTML 字符
    cache: true,      // 是否开启缓存（依赖 options 的 filename 字段）
    compress: false,  // 是否压缩输出
    parser: null      // 自定义语法格式器 @see: template-syntax.js
    */
    var debug = options.debug;
    var openTag = options.openTag;
    var closeTag = options.closeTag;
    var parser = options.parser;
    var compress = options.compress;
    var escape = options.escape;

    var line = 1;
    var uniq = {$data:1,$filename:1,$utils:1,$helpers:1,$out:1,$line:1};

    //isNewEngin在6-8返回undefined
    var isNewEngine = &#39;&#39;.trim;// &#39;proto&#39; in {}
    var replaces = isNewEngine
    ? ["$out=&#39;&#39;;", "$out+=", ";", "$out"]
    : ["$out=[];", "$out.push(", ");", "$out.join(&#39;&#39;)"];

    var concat = isNewEngine
        ? "$out+=text;return $out;"
        : "$out.push(text);";

    var print = "function(){"
    +      "var text=&#39;&#39;.concat.apply(&#39;&#39;,arguments);"
    +       concat
    +  "}";

    var include = "function(filename,data){"
    +      "data=data||$data;"
    +      "var text=$utils.$include(filename,data,$filename);"
    +       concat
    +   "}";

    var headerCode = "&#39;use strict&#39;;"
    + "var $utils=this,$helpers=$utils.$helpers,"
    + (debug ? "$line=0," : "");

    var mainCode = replaces[0];

    var footerCode = "return new String(" + replaces[3] + ");"

    // html与逻辑语法分离
    forEach(source.split(openTag), function (code) {
        code = code.split(closeTag);

        var $0 = code[0];
        var $1 = code[1];

        // code: [html]
        if (code.length === 1) {

            mainCode += html($0);

        // code: [logic, html]
        } else {

            mainCode += logic($0);

            if ($1) {
                mainCode += html($1);
            }
        }

    });

    var code = headerCode + mainCode + footerCode;

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上例中模板中的模板字符串代码会被拼接成如下字符串：

&#39;use strict&#39;;
var $utils   = this,
	$helpers = $utils.$helpers,
	isAdmin  = $data.isAdmin,
	$escape  = $utils.$escape,
	title    = $data.title,
	$each    = $utils.$each,
	user     = $data.user,
	name     = $data.name,
	i        = $data.i,
	$out     = &#39;&#39;;

if (isAdmin) {
	$out += &#39;\n\n	<h1>&#39;;
	$out += $escape(title);
	$out += &#39;</h1>\n	<ul>\n	    &#39;;
	$each(user, function(name, i) {
		$out += &#39;\n	        <li>&#39;;
		$out += $escape(i + 1);
		$out += &#39; ：&#39;;
		$out += $escape(name);
		$out += &#39;</li>\n	    &#39;;
	});
	$out += &#39;\n	</ul>\n\n	&#39;;
}
return new String($out);

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然后会被生成如下函数：

var Render = new Function("$data", "$filename", code);

/*Outputs:
function anonymous($data, $filename) {
	&#39;use strict&#39;;
	var $utils   = this,
		$helpers = $utils.$helpers,
		isAdmin  = $data.isAdmin,
		$escape  = $utils.$escape,
		title    = $data.title,
		$each    = $utils.$each,
		user     = $data.user,
		name     = $data.name,
		i        = $data.i,
		$out     = &#39;&#39;;
	if (isAdmin) {
		$out += &#39;\n\n	<h1>&#39;;
		$out += $escape(title);
		$out += &#39;</h1>\n	<ul>\n	    &#39;;
		$each(user, function(name, i) {
			$out += &#39;\n	        <li>&#39;;
			$out += $escape(i + 1);
			$out += &#39; ：&#39;;
			$out += $escape(name);
			$out += &#39;</li>\n	    &#39;;
		});
		$out += &#39;\n	</ul>\n\n	&#39;;
	}
	return new String($out);
}
 */
console.log(Render);

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2.5 装载数据，视图呈现

/*Outputs:
<h1>User lists</h1>
<ul>
    <li>1 ：zuojj</li>
    <li>2 ：Benjamin</li>
    <li>3 ：John</li>
    <li>4 ：Rubby</li>
    <li>5 ：Handy</li>
    <li>6 ：CIMI</li> 
</ul>
*/
console.log(new Render(data, filename) + &#39;&#39;);
//对象转换为字符串
return new Render(data, filename) + &#39;&#39;;

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三、常见JavaScript模板引擎及测试对比

BaiduTemplate —— 最简单好用的JS模板引擎(百度)
artTemplate —— 高性能JavaScript模板引擎(腾讯CDC)
Velocity.js —— 来自淘宝的JS 模板引擎
JavaScript Templates —— 轻量、快速、强大、无依赖模板引擎
Juicer —— 高效、轻量的Javascript模板引擎
mustache.js —— Logic-less {{mustache}} templates with JavaScript
各大Javascript模板引擎测试对比

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