JavaScript模板引擎应用场景及实现原理详解

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

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

defaults.parser = function (code, options) {
  // var match = code.match(/([\w\$]*)(\b.*)/);
  // var key = match[1];
  // var args = match[2];
  // var split = args.split(' ');
  // split.shift();
  //if isAdmin
  code = code.replace(/^\s/, '');
  //["if", "isAdmin"]
  var split = code.split(' ');
  //if
  var key = split.shift();
  //isAdmin
  var args = split.join(' ');
  switch (key) {
    case 'if':
      //if(isAdmin){
      code = 'if(' + args + '){';
      break;
    case 'else':
      if (split.shift() === 'if') {
        split = ' if(' + split.join(' ') + ')';
      } else {
        split = '';
      }
      code = '}else' + split + '{';
      break;
    case '/if':
      code = '}';
      break;
    case 'each':
      var object = split[0] || '$data';
      var as   = split[1] || 'as';
      var value = split[2] || '$value';
      var index = split[3] || '$index';
      var param  = value + ',' + index;
      if (as !== 'as') {
        object = '[]';
      }
      code = '$each(' + object + ',function(' + param + '){';
      break;
    case '/each':
      code = '});';
      break;
    case 'echo':
      code = 'print(' + args + ');';
      break;
    case 'print':
    case 'include':
      code = key + '(' + split.join(',') + ');';
      break;

function compiler (source, options) {
  /*
  openTag: '<%',  // 逻辑语法开始标签
  closeTag: '%>',  // 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 = ''.trim;// '__proto__' in {}
  var replaces = isNewEngine
  ? ["$out='';", "$out+=", ";", "$out"]
  : ["$out=[];", "$out.push(", ");", "$out.join('')"];
  var concat = isNewEngine
    ? "$out+=text;return $out;"
    : "$out.push(text);";
  var print = "function(){"
  +   "var text=''.concat.apply('',arguments);"
  +    concat
  + "}";
  var include = "function(filename,data){"
  +   "data=data||$data;"
  +   "var text=$utils.$include(filename,data,$filename);"
  +    concat
  +  "}";
  var headerCode = "'use strict';"
  + "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;

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

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

/*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) + '');
//对象转换为字符串
return new Render(data, filename) + '';