vue.js源码学习分享，七

var _Set;
/* istanbul ignore if */
if (typeof Set !== 'undefined' && isNative(Set)) {
  // use native Set when available.//当本地set有效时使用set
  _Set = Set;
} else {
  // a non-standard Set polyfill that only works with primitive keys.//一个不标准的set只会和一些简单的键工作
  _Set = (function () {
    function Set () {
      this.set = Object.create(null);
    }
    Set.prototype.has = function has (key) {
      return this.set[key] === true
    };
    Set.prototype.add = function add (key) {
      this.set[key] = true;
    };
    Set.prototype.clear = function clear () {
      this.set = Object.create(null);
    };

    return Set;
  }());
}

var perf;//性能

{//代码块这是es6中的，代替了立即执行匿名函数
  perf = inBrowser && window.performance;//Web Performance API允许网页访问某些函数来测量网页和Web应用程序的性能，包括 Navigation Timing API和高分辨率时间数据。
  if (perf && (!perf.mark || !perf.measure)) {
    perf = undefined;
  }
}

/*  */

var emptyObject = Object.freeze({});//冻结一个空的对象

/**
 * Check if a string starts with $ or _//检查一个字符串是否以$或者下划线为开头
 */
function isReserved (str) {
  var c = (str + '').charCodeAt(0);//把参数转为字符串获取第一个字符
  return c === 0x24 || c === 0x5F
}

/**
 * Define a property.//定义一个属性
 */
function def (obj, key, val, enumerable) {
  Object.defineProperty(obj, key, {//Object.defineProperty给对象定义属性
    value: val,
    enumerable: !!enumerable,
    writable: true,
    configurable: true
  });
}

/**
 * Parse simple path.//解析简单的路径
 */
var bailRE = /[^\w.$]/;
function parsePath (path) {
  if (bailRE.test(path)) {
    return
  } else {
    var segments = path.split('.');
    return function (obj) {
      for (var i = 0; i < segments.length; i++) {
        if (!obj) { return }
        obj = obj[segments[i]];
      }
      return obj
    }
  }
}

var warn = noop;
var tip = noop;
var formatComponentName;

{
  var hasConsole = typeof console !== 'undefined';
  var classifyRE = /(?:^|[-_])(\w)/g;
  var classify = function (str) { return str
    .replace(classifyRE, function (c) { return c.toUpperCase(); })
    .replace(/[-_]/g, ''); };

  warn = function (msg, vm) {
    if (hasConsole && (!config.silent)) {
      console.error("[Vue warn]: " + msg + " " + (
        vm ? formatLocation(formatComponentName(vm)) : ''
      ));
    }
  };

  tip = function (msg, vm) {
    if (hasConsole && (!config.silent)) {
      console.warn("[Vue tip]: " + msg + " " + (
        vm ? formatLocation(formatComponentName(vm)) : ''
      ));
    }
  };

  formatComponentName = function (vm, includeFile) {//格式化组件名称
    if (vm.$root === vm) {
      return '<Root>'
    }
    var name = vm._isVue
      ? vm.$options.name || vm.$options._componentTag
      : vm.name;

    var file = vm._isVue && vm.$options.__file;
    if (!name && file) {
      var match = file.match(/([^/\\]+)\.vue$/);
      name = match && match[1];
    }

    return (
      (name ? ("<" + (classify(name)) + ">") : "<Anonymous>") +
      (file && includeFile !== false ? (" at " + file) : '')
    )
  };

  var formatLocation = function (str) {
    if (str === "<Anonymous>") {
      str += " - use the \"name\" option for better debugging messages.";
    }
    return ("\n(found in " + str + ")")
  };
}