vue.js源码学习分享，四

/**
 * Generate a static keys string from compiler modules.//从编译器生成一个静态键字符串模块。
 */
function genStaticKeys (modules) {
  return modules.reduce(function (keys, m) {
    return keys.concat(m.staticKeys || [])
  }, []).join(',')
}

/**
 * Check if two values are loosely equal - that is,
 * if they are plain objects, do they have the same shape?
 *///检查两个值是否相等
function looseEqual (a, b) {
  var isObjectA = isObject(a);
  var isObjectB = isObject(b);
  if (isObjectA && isObjectB) {
    return JSON.stringify(a) === JSON.stringify(b)
  } else if (!isObjectA && !isObjectB) {
    return String(a) === String(b)
  } else {
    return false
  }
}
//获取val在arr中的位置
function looseIndexOf (arr, val) {
  for (var i = 0; i < arr.length; i++) {
    if (looseEqual(arr[i], val)) { return i }
  }
  return -1
}

/**
 * Ensure a function is called only once.//保证函数只执行一次
 */
function once (fn) {
  var called = false;
  return function () {
    if (!called) {
      called = true;
      fn();
    }
  }
}