EJS 项目源码阅读

Question

ejs 项目大名鼎鼎，应该就不需要介绍了，主要收获就是得知了实现一个模板引擎的流程，ejs 是将模板作为字符串逐个解析，遇到正常的 html 代码，就放进一个数组中去，遇到 js 代码则进行过滤器、包含等的处理，最后数组 join 成一个可以成为 Function 构造函数第二个参数的字符串，构造成构造函数之后就是调用返回最终的 html 字符串。以下是阅读源码的笔记，因为源码中遗憾有很多说明，所以笔记很少。

ejs = (function(){

// CommonJS require()

function require(p){
    if ('fs' == p) return {};
    if ('path' == p) return {};
    var path = require.resolve(p)
      , mod = require.modules[path];
    if (!mod) throw new Error('failed to require "' + p + '"');
    if (!mod.exports) {
      mod.exports = {};
      mod.call(mod.exports, mod, mod.exports, require.relative(path));
    }
    return mod.exports;
  }

require.modules = {};

require.resolve = function (path){
    var orig = path
      , reg = path + '.js'
      , index = path + '/index.js';
    return require.modules[reg] && reg
      || require.modules[index] && index
      || orig;
  };

require.register = function (path, fn){
    require.modules[path] = fn;
  };

require.relative = function (parent) {
    return function(p){
      if ('.' != p.substr(0, 1)) return require(p);
      
      var path = parent.split('/')
        , segs = p.split('/');
      path.pop();
      
      for (var i = 0; i < segs.length; i++) {
        var seg = segs[i];
        if ('..' == seg) path.pop();
        else if ('.' != seg) path.push(seg);
      }

      return require(path.join('/'));
    };
  };


require.register("ejs.js", function(module, exports, require){

/*!
 * EJS
 * Copyright(c) 2012 TJ Holowaychuk <tj@vision-media.ca>
 * MIT Licensed
 */

/**
 * Module dependencies.
 */

var utils = require('./utils')
  , path = require('path')
  , dirname = path.dirname
  , extname = path.extname
  , join = path.join
  , fs = require('fs')
  , read = fs.readFileSync;

/**
 * Filters.
 *
 * @type Object
 */

var filters = exports.filters = require('./filters');

/**
 * Intermediate js cache.
 *
 * @type Object
 */

var cache = {};

/**
 * Clear intermediate js cache.
 *
 * @api public
 */

exports.clearCache = function(){
  cache = {};
};

/**
 * Translate filtered code into function calls.
 *
 * @param {String} js
 * @return {String}
 * @api private
 */

function filtered(js) {
  return js.substr(1).split('|').reduce(function(js, filter){
    var parts = filter.split(':')
      , name = parts.shift()
      , args = parts.join(':') || '';
    if (args) args = ', ' + args;
    return 'filters.' + name + '(' + js + args + ')';
  });
};

/**
 * Re-throw the given `err` in context to the
 * `str` of ejs, `filename`, and `lineno`.
 *
 * @param {Error} err
 * @param {String} str
 * @param {String} filename
 * @param {String} lineno
 * @api private
 */

function rethrow(err, str, filename, lineno){
  var lines = str.split('n')
    , start = Math.max(lineno - 3, 0)
    , end = Math.min(lines.length, lineno + 3);

  // Error context
  var context = lines.slice(start, end).map(function(line, i){
    var curr = i + start + 1;
    return (curr == lineno ? ' >> ' : '    ')
      + curr
      + '| '
      + line;
  }).join('n');

  // Alter exception message
  err.path = filename;
  err.message = (filename || 'ejs') + ':'
    + lineno + 'n'
    + context + 'nn'
    + err.message;

  throw err;
}

/**
 * Parse the given `str` of ejs, returning the function body.
 *
 * @param {String} str
 * @return {String}
 * @api public
 */

var parse = exports.parse = function(str, options){
  var options = options || {}
    , open = options.open || exports.open || '<%'
    , close = options.close || exports.close || '%>'
    , filename = options.filename
    , compileDebug = options.compileDebug !== false
    , buf = "";

  buf += 'var buf = [];';
  if (false !== options._with) buf += 'nwith (locals || {}) { (function(){ ';
  buf += 'n buf.push('';

  var lineno = 1;

  var consumeEOL = false;
  for (var i = 0, len = str.length; i < len; ++i) {
    var stri = str[i];
    if (str.slice(i, open.length + i) == open) {
      i += open.length

      var prefix, postfix, line = (compileDebug ? '__stack.lineno=' : '') + lineno;
      switch (str[i]) {
        case '=':
          prefix = "', escape((" + line + ', ';
          postfix = ")), '";
          ++i;
          break;
        case '-':
          prefix = "', (" + line + ', ';
          postfix = "), '";
          ++i;
          break;
        default:
          prefix = "');" + line + ';';
          postfix = "; buf.push('";
      }

      // 查找对应的结尾
      var end = str.indexOf(close, i);

      if (end < 0){
        throw new Error('Could not find matching close tag "' + close + '".');
      }

      // 提取模板中的js代码
      var js = str.substring(i, end)
        , start = i
        , include = null
        , n = 0;

      // 结尾-表示不需要转义，这种情况<%- code -%>
      if ('-' == js[js.length-1]){
        js = js.substring(0, js.length - 2);
        consumeEOL = true;
      }

      // 处理调用include情况 <%- include() %>
      if (0 == js.trim().indexOf('include')) {
        var name = js.trim().slice(7).trim();
        if (!filename) throw new Error('filename option is required for includes');
        var path = resolveInclude(name, filename);
        include = read(path, 'utf8');
        include = exports.parse(include, { filename: path, _with: false, open: open, close: close, compileDebug: compileDebug });
        buf += "' + (function(){" + include + "})() + '";
        js = '';
      }

      // 处理js代码换行的情况，又路遇装逼犯，~(n = js.indexOf("n", n))就是存在换行符情况之下执行
      while (~(n = js.indexOf("n", n))) n++, lineno++;
      // 过滤器处理，<%=: users | map:'name' | join %>
        if (js.substr(0, 1) == ':') js = filtered(js);
      if (js) {
        if (js.lastIndexOf('//') > js.lastIndexOf('n')) js += 'n';
        buf += prefix;
        buf += js;
        buf += postfix;
      }
      i += end - start + close.length - 1;

    } else if (stri == "\") {
      buf += "\\";
    } else if (stri == "'") {
      buf += "\'";
    } else if (stri == "r") {
      // ignore
    } else if (stri == "n") {
      if (consumeEOL) {
        consumeEOL = false;
      } else {
        buf += "\n";
        lineno++;
      }
    } else {
      buf += stri;
    }
  }

  if (false !== options._with) buf += "'); })();n} nreturn buf.join('');";
  else buf += "');nreturn buf.join('');";
  return buf;
};

/**
 * Compile the given `str` of ejs into a `Function`.
 *
 * @param {String} str
 * @param {Object} options
 * @return {Function}
 * @api public
 */

var compile = exports.compile = function(str, options){
  options = options || {};
  var escape = options.escape || utils.escape;

  var input = JSON.stringify(str)
    , compileDebug = options.compileDebug !== false
    , client = options.client
    , filename = options.filename
        ? JSON.stringify(options.filename)
        : 'undefined';

  if (compileDebug) {
    // Adds the fancy stack trace meta info
    str = [
      'var __stack = { lineno: 1, input: ' + input + ', filename: ' + filename + ' };',
      rethrow.toString(),
      'try {',
      exports.parse(str, options),
      '} catch (err) {',
      '  rethrow(err, __stack.input, __stack.filename, __stack.lineno);',
      '}'
    ].join("n");
  } else {
    str = exports.parse(str, options);
  }

  if (options.debug) console.log(str);
  if (client) str = 'escape = escape || ' + escape.toString() + ';n' + str;

  try {
    // 别忘了，可以使用构造函数定义函数呀
    var fn = new Function('locals, filters, escape, rethrow', str);
  } catch (err) {
    if ('SyntaxError' == err.name) {
      err.message += options.filename
        ? ' in ' + filename
        : ' while compiling ejs';
    }
    throw err;
  }

  if (client) return fn;

  return function(locals){
    return fn.call(this, locals, filters, escape, rethrow);
  }
};

/**
 * Render the given `str` of ejs.
 *
 * Options:
 *
 *   - `locals`          Local variables object
 *   - `cache`           Compiled functions are cached, requires `filename`
 *   - `filename`        Used by `cache` to key caches
 *   - `scope`           Function execution context
 *   - `debug`           Output generated function body
 *   - `open`            Open tag, defaulting to "<%"
 *   - `close`           Closing tag, defaulting to "%>"
 *
 * @param {String} str
 * @param {Object} options
 * @return {String}
 * @api public
 */

// 渲染函数
exports.render = function(str, options){
  var fn
    , options = options || {};

  // 检查是否缓存
  if (options.cache) {
    if (options.filename) {
      fn = cache[options.filename] || (cache[options.filename] = compile(str, options));
    } else {
      throw new Error('"cache" option requires "filename".');
    }
  } else {
    fn = compile(str, options);
  }

  options.__proto__ = options.locals;
  return fn.call(options.scope, options);
};

/**
 * Render an EJS file at the given `path` and callback `fn(err, str)`.
 *
 * @param {String} path
 * @param {Object|Function} options or callback
 * @param {Function} fn
 * @api public
 */

exports.renderFile = function(path, options, fn){
  var key = path + ':string';

  if ('function' == typeof options) {
    fn = options, options = {};
  }

  options.filename = path;

  var str;
  try {
    str = options.cache
      ? cache[key] || (cache[key] = read(path, 'utf8'))
      : read(path, 'utf8');
  } catch (err) {
    fn(err);
    return;
  }
  fn(null, exports.render(str, options));
};

/**
 * Resolve include `name` relative to `filename`.
 *
 * @param {String} name
 * @param {String} filename
 * @return {String}
 * @api private
 */

function resolveInclude(name, filename) {
  var path = join(dirname(filename), name);
  var ext = extname(name);
  if (!ext) path += '.ejs';
  return path;
}

// express support

exports.__express = exports.renderFile;

/**
 * Expose to require().
 */

if (require.extensions) {
  require.extensions['.ejs'] = function (module, filename) {
    filename = filename || module.filename;
    var options = { filename: filename, client: true }
      , template = fs.readFileSync(filename).toString()
      , fn = compile(template, options);
    module._compile('module.exports = ' + fn.toString() + ';', filename);
  };
} else if (require.registerExtension) {
  require.registerExtension('.ejs', function(src) {
    return compile(src, {});
  });
}

}); // module: ejs.js

require.register("filters.js", function(module, exports, require){
/*!
 * EJS - Filters
 * Copyright(c) 2010 TJ Holowaychuk <tj@vision-media.ca>
 * MIT Licensed
 */

/**
 * First element of the target `obj`.
 */

// 过滤函数
exports.first = function(obj) {
  return obj[0];
};

/**
 * Last element of the target `obj`.
 */
// 过滤函数
exports.last = function(obj) {
  return obj[obj.length - 1];
};

/**
 * Capitalize the first letter of the target `str`.
 */
// 过滤函数
exports.capitalize = function(str){
  str = String(str);
  return str[0].toUpperCase() + str.substr(1, str.length);
};

/**
 * Downcase the target `str`.
 */
// 过滤函数
exports.downcase = function(str){
  return String(str).toLowerCase();
};

/**
 * Uppercase the target `str`.
 */
// 过滤函数
exports.upcase = function(str){
  return String(str).toUpperCase();
};

/**
 * Sort the target `obj`.
 */
// 过滤函数
exports.sort = function(obj){
  return Object.create(obj).sort();
};

/**
 * Sort the target `obj` by the given `prop` ascending.
 */

exports.sort_by = function(obj, prop){
  return Object.create(obj).sort(function(a, b){
    a = a[prop], b = b[prop];
    if (a > b) return 1;
    if (a < b) return -1;
    return 0;
  });
};

/**
 * Size or length of the target `obj`.
 */

exports.size = exports.length = function(obj) {
  return obj.length;
};

/**
 * Add `a` and `b`.
 */

exports.plus = function(a, b){
  return Number(a) + Number(b);
};

/**
 * Subtract `b` from `a`.
 */

exports.minus = function(a, b){
  return Number(a) - Number(b);
};

/**
 * Multiply `a` by `b`.
 */

exports.times = function(a, b){
  return Number(a) * Number(b);
};

/**
 * Divide `a` by `b`.
 */

exports.divided_by = function(a, b){
  return Number(a) / Number(b);
};

/**
 * Join `obj` with the given `str`.
 */

exports.join = function(obj, str){
  return obj.join(str || ', ');
};

/**
 * Truncate `str` to `len`.
 */

exports.truncate = function(str, len, append){
  str = String(str);
  if (str.length > len) {
    str = str.slice(0, len);
    if (append) str += append;
  }
  return str;
};

/**
 * Truncate `str` to `n` words.
 */

exports.truncate_words = function(str, n){
  var str = String(str)
    , words = str.split(/ +/);
  return words.slice(0, n).join(' ');
};

/**
 * Replace `pattern` with `substitution` in `str`.
 */

exports.replace = function(str, pattern, substitution){
  return String(str).replace(pattern, substitution || '');
};

/**
 * Prepend `val` to `obj`.
 */

exports.prepend = function(obj, val){
  return Array.isArray(obj)
    ? [val].concat(obj)
    : val + obj;
};

/**
 * Append `val` to `obj`.
 */

exports.append = function(obj, val){
  return Array.isArray(obj)
    ? obj.concat(val)
    : obj + val;
};

/**
 * Map the given `prop`.
 */

exports.map = function(arr, prop){
  return arr.map(function(obj){
    return obj[prop];
  });
};

/**
 * Reverse the given `obj`.
 */

exports.reverse = function(obj){
  return Array.isArray(obj)
    ? obj.reverse()
    : String(obj).split('').reverse().join('');
};

/**
 * Get `prop` of the given `obj`.
 */

exports.get = function(obj, prop){
  return obj[prop];
};

/**
 * Packs the given `obj` into json string
 */
exports.json = function(obj){
  return JSON.stringify(obj);
};

}); // module: filters.js

require.register("utils.js", function(module, exports, require){

/*!
 * EJS
 * Copyright(c) 2010 TJ Holowaychuk <tj@vision-media.ca>
 * MIT Licensed
 */

/**
 * Escape the given string of `html`.
 *
 * @param {String} html
 * @return {String}
 * @api private
 */

exports.escape = function(html){
  return String(html)
    .replace(/&/g, '&')
    .replace(/</g, '<')
    .replace(/>/g, '>')
    .replace(/'/g, ''')
    .replace(/"/g, '"');
};
 

}); // module: utils.js

 return require("ejs");
})();