vue源码笔记

// 缓存一个对某个字符串执行某个计算规则的结果，避免重复计算带来的开销

function cached (fn) {
    var cache = Object.create(null);
    return (function cachedFn (str) {
        var hit = cache[str];
        return hit || (cache[str] = fn(str))
    })
}

内部应用example：

// 以-为分隔的字符串 => 驼峰转换
var camelizeRE = /-(\w)/g;
var camelize = cached(function (str) {
    return str.replace(camelizeRE, function (_, c) { return c ? c.toUpperCase() : ''; })
});

array every some

// 确保方法只执行一次
function once (fn) {
    var called = false;
    return function () {
        if (!called) {
            called = true;
            fn.apply(this, arguments);
        }
    }
}

生命周期钩子：

var LIFECYCLE_HOOKS = [
        'beforeCreate',
        'created',
        'beforeMount',
        'mounted',
        'beforeUpdate',
        'updated',
        'beforeDestroy',
        'destroyed',
        'activated',
        'deactivated',
        'errorCaptured'
    ];

// 暂时还不知道有何作用
var bailRE = /[^\w.$]/;
function parsePath (path) {
  if (bailRE.test(path)) {
    return
  }
  var segments = path.split('.');
  return function (obj) {
    for (var i = 0; i < segments.length; i++) {
      if (!obj) { return }
      obj = obj[segments[i]];
    }
    return obj
  }
}

各种环境判断方法

// Browser environment sniffing
    var inBrowser = typeof window !== 'undefined';
    var inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform;
    var weexPlatform = inWeex && WXEnvironment.platform.toLowerCase();
    var UA = inBrowser && window.navigator.userAgent.toLowerCase();
    var isIE = UA && /msie|trident/.test(UA);
    var isIE9 = UA && UA.indexOf('msie 9.0') > 0;
    var isEdge = UA && UA.indexOf('edge/') > 0;
    var isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android');
    var isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios');
    var isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge;

这里为什么要加()

// Firefox has a "watch" function on Object.prototype...
    var nativeWatch = ({}).watch;