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vue源码前708行的工具方法汇总

主要记录vue源码里面的骚操作

1、判断参数是否是undefined,true and false

    function isUndef (v) {
      return v === undefined || v === null
    }
    function isDef (v) {
      return v !== undefined && v !== null
    }
  
    function isTrue (v) {
      return v === true
    }
  
    function isFalse (v) {
      return v === false
    }
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--- test

    isUndef('123')
    //false
    isUndef('')
    //false
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2、判断一个数据是否是基础类型

    /**
     * Check if value is primitive(基础类型). 
     */
    function isPrimitive (value) {
      return (
        typeof value === 'string' ||
        typeof value === 'number' ||
        // $flow-disable-line
        typeof value === 'symbol' ||
        typeof value === 'boolean'
      )
    }
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3、对象检测

    function isObject (obj) {
      return obj !== null && typeof obj === 'object'
    }
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4、判断一个对象是啥类型

    /**
     * Get the raw type string of a value, e.g., [object Object].
     */
    var _toString = Object.prototype.toString;
  
    function toRawType (value) {
      return _toString.call(value).slice(8, -1)  //返回第八开始截取的数据类型
    }

    function isPlainObject (obj) {
      return _toString.call(obj) === '[object Object]' //检测数据是否为对象Object
    }
  
    function isRegExp (v) {
      return _toString.call(v) === '[object RegExp]' //检测数据是够为正则表达式
    }
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5、判断是否是有效的数组索引

    /**
     * Check if val is a valid array index.
     */
    function isValidArrayIndex (val) {
      var n = parseFloat(String(val)); //字符串转化数字 
      return n >= 0 && Math.floor(n) === n && isFinite(val)
    }
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6、判断是否是promise函数

    function isPromise (val) {
      return (
        isDef(val) &&
        typeof val.then === 'function' &&
        typeof val.catch === 'function'
      )
    }
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7、把一个值转化为字符串

    /**
     * Convert a value to a string that is actually rendered.
     */
    function toString (val) {
      return val == null
        ? ''
        : Array.isArray(val) || (isPlainObject(val) && val.toString === _toString)
          ? JSON.stringify(val, null, 2)
          : String(val)
    }
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8、把数字转化为字符串

    function toNumber (val) {
      var n = parseFloat(val);
      return isNaN(n) ? val : n
    }
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9、判断指定的字符是否在map的key里面

    /**
     * Make a map and return a function for checking if a key
     * is in that map.
     */
    function makeMap (
      str,
      expectsLowerCase
    ) {
      var map = Object.create(null);
      var list = str.split(',');
      for (var i = 0; i < list.length; i++) {
        map[list[i]] = true;
      }
      return expectsLowerCase
        ? function (val) { return map[val.toLowerCase()]; }
        : function (val) { return map[val]; }
    }

    /**
     * Check if a tag is a built-in tag.
     */
    var isBuiltInTag = makeMap('slot,component', true);
  
    /**
     * Check if an attribute is a reserved attribute.
     */
    var isReservedAttribute = makeMap('key,ref,slot,slot-scope,is');
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10、从数组里面移除指定的一项

     /**
     * Remove an item from an array.
     */
    function remove (arr, item) {
      if (arr.length) {
        var index = arr.indexOf(item); //找到该项的索引值
        if (index > -1) { //存在该项
          return arr.splice(index, 1)
        }
      }
    }
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11、hasOwnProperty() 方法会返回一个布尔值,指示对象自身属性中是否具有指定的属性(也就是,是否有指定的键)。

    /**
     * Check whether an object has the property.
     */
    var hasOwnProperty = Object.prototype.hasOwnProperty;
    function hasOwn (obj, key) {
      return hasOwnProperty.call(obj, key)
    }
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12、缓存数据

    /**
     * Create a cached version of a pure function.
     */
    function cached (fn) {
      var cache = Object.create(null);
      return (function cachedFn (str) {
        var hit = cache[str];
        return hit || (cache[str] = fn(str))
      })
    }
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13、 将连字符-连接的字符串转化成驼峰标识的字符串

    var camelizeRE = /-(\w)/g;
    var camelize = cached(function (str) {
      return str.replace(camelizeRE, function (_, c) { return c ? c.toUpperCase() : ''; })
    });
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14、首字符大写

    /**
     * Capitalize a string.
     */
    var capitalize = cached(function (str) {
      return str.charAt(0).toUpperCase() + str.slice(1)
    });
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15、驼峰的字符串转化为连字符

    /**
     * Hyphenate a camelCase string.
     */
    var hyphenateRE = /\B([A-Z])/g;
    var hyphenate = cached(function (str) {
      return str.replace(hyphenateRE, '-$1').toLowerCase()
    });
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16、改变函数执行上下文

    /* istanbul ignore next */
    function polyfillBind (fn, ctx) {
      function boundFn (a) {
        var l = arguments.length;
        return l
          ? l > 1
            ? fn.apply(ctx, arguments)
            : fn.call(ctx, a)
          : fn.call(ctx)
      }
  
      boundFn._length = fn.length;
      return boundFn
    }
  
    function nativeBind (fn, ctx) {
      return fn.bind(ctx)
    }
  
    var bind = Function.prototype.bind
      ? nativeBind
      : polyfillBind;
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17、类数组转化为数组

    /**
     * Convert an Array-like object to a real Array.
     */
    function toArray (list, start) {
      start = start || 0;
      var i = list.length - start;
      var ret = new Array(i);
      while (i--) {
        ret[i] = list[i + start];
      }
      return ret
    }
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18、复制对象的属性

    /**
     * Mix properties into target object.
     */
    function extend (to, _from) {
      for (var key in _from) {
        to[key] = _from[key];
      }
      return to
    }
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19、把数组转化为对象

    /**
     * Merge an Array of Objects into a single Object.
     */
    function toObject (arr) {
      var res = {};
      for (var i = 0; i < arr.length; i++) {
        if (arr[i]) {
          extend(res, arr[i]);
        }
      }
      return res
    }
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20、比较两个数值是否相等

    /**
     * Check if two values are loosely equal - that is,
     * if they are plain objects, do they have the same shape?
     */
    function looseEqual (a, b) {
      if (a === b) { return true }
      var isObjectA = isObject(a);
      var isObjectB = isObject(b);
      if (isObjectA && isObjectB) {
        try {
          var isArrayA = Array.isArray(a);
          var isArrayB = Array.isArray(b);
          if (isArrayA && isArrayB) {
            return a.length === b.length && a.every(function (e, i) {
              return looseEqual(e, b[i])
            })
          } else if (a instanceof Date && b instanceof Date) {
            return a.getTime() === b.getTime()
          } else if (!isArrayA && !isArrayB) {
            var keysA = Object.keys(a);
            var keysB = Object.keys(b);
            return keysA.length === keysB.length && keysA.every(function (key) {
              return looseEqual(a[key], b[key])
            })
          } else {
            /* istanbul ignore next */
            return false
          }
        } catch (e) {
          /* istanbul ignore next */
          return false
        }
      } else if (!isObjectA && !isObjectB) {
        return String(a) === String(b)
      } else {
        return false
      }
    }

    function looseIndexOf (arr, val) {
      for (var i = 0; i < arr.length; i++) {
        if (looseEqual(arr[i], val)) { return i }
      }
      return -1
    }
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21、只让函数调用一次

    /**
     * Ensure a function is called only once.
     */
    function once (fn) {
      var called = false;
      return function () {
        if (!called) {
          called = true;
          fn.apply(this, arguments);
        }
      }
    }
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22、判断字符是否以$/_开始

    /**
     * Check if a string starts with $ or _
     */
    function isReserved (str) {
      var c = (str + '').charCodeAt(0);
      return c === 0x24 || c === 0x5F
    }
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23、定义一个属性

    /**
     * Define a property.
     */
    function def (obj, key, val, enumerable) {
      Object.defineProperty(obj, key, {
        value: val,
        enumerable: !!enumerable,
        writable: true,
        configurable: true
      });
    }
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24、解析一个简单的路径

    /**
     * Parse simple path.
     */
    var bailRE = new RegExp(("[^" + (unicodeRegExp.source) + ".$_\\d]"));
    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
      }
    }
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25、各种平台的类型判断

// can we use __proto__?
    var hasProto = '__proto__' in {};
  
    // 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;
    var isPhantomJS = UA && /phantomjs/.test(UA);
    var isFF = UA && UA.match(/firefox\/(\d+)/);
  
    // Firefox has a "watch" function on Object.prototype...
    var nativeWatch = ({}).watch;
  
    var supportsPassive = false;
    if (inBrowser) {
      try {
        var opts = {};
        Object.defineProperty(opts, 'passive', ({
          get: function get () {
            /* istanbul ignore next */
            supportsPassive = true;
          }
        })); // https://github.com/facebook/flow/issues/285
        window.addEventListener('test-passive', null, opts);
      } catch (e) {}
    }
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26、字符串重复指定的次数

        var repeat = function (str, n) {
        var res = '';
        while (n) {
          if (n % 2 === 1) { res += str; }
          if (n > 1) { str += str; }
          n >>= 1;
        }
        return res
      };
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vue源码前708行的工具方法汇总