underscore.js源码进修collection

// Internal function that returns an efficient (for current engines) version
// of the passed-in callback, to be repeatedly applied in other Underscore
// functions.
// 内部复用函数，用于转变函数上下文。

var optimizeCb = function(func, context, argCount) {
//context为undefined状况下，直接返回func
// void 0
// 实行历程：1，对右边表达式求值。2.返回undefined
// 为什么如许节外生枝：js中，undefined不是保留字，能够建立windows.undefined=anything.void返回undefined较平安。
// 用途：1返回undefined。2a标签不跳转href=Javascript:(void 0)3img空图片src=Javascript:(void 0)
if (cOntext=== void 0) return func;
//有传入context状况下，将func上下文改成context
switch (argCount == null ? 3 : argCount) {
case 1:
return function(value) {
return func.call(context, value);
};
// The 2-argument case is omitted because we’re not using it.
case 3:
return function(value, index, collection) {
return func.call(context, value, index, collection);
};
//_.reduce中运用
case 4:
return function(accumulator, value, index, collection) {
return func.call(context, accumulator, value, index, collection);
};
}
return function() {
return func.apply(context, arguments);
};
};
var builtinIteratee;


// An internal function to generate callbacks that can be applied to each
// element in a collection, returning the desired result — either identity,
// an arbitrary callback, a property matcher, or a property accessor.
// 内部函数，天生适用于鸠合每一个元素的回调函数
// 传入null等空值，获得等价函数
// 传入function，获得绑定了上下文的函数
// 传入对象，获得婚配函数
// 传入其他，获得属性接见函数

var cb = function(value, context, argCount) {
//?？是何意图？？
if (_.iteratee !== builtinIteratee) return _.iteratee(value, context);
//返回null
if (value == null) return _.identity;
//假如是函数，绑定函数上下文
if (_.isFunction(value)) return optimizeCb(value, context, argCount);
//假如是对象，返回婚配函数
if (_.isObject(value) && !_.isArray(value)) return _.matcher(value);
//返回猎取属性值函数
return _.property(value);
};


// External wrapper for our callback generator. Users may customize
// _.iteratee if they want additional predicate/iteratee shorthand styles.
// This abstraction hides the internal-only argCount argument.
// 外部函数，返回cb函数效果

_.iteratee = builtinIteratee = function(value, context) {
return cb(value, context, Infinity);
};


// Some functions take a variable number of arguments, or a few expected
// arguments at the beginning and then a variable number of values to operate
// on. This helper accumulates all remaining arguments past the function’s
// argument length (or an explicit startIndex), into an array that becomes
// the last argument. Similar to ES6’s &＃8220;rest parameter&＃8221;.
// 用于实参个数不定的函数的牢固参数及盈余参数整顿。
// example:_.invoke
// func.length=3，so startIndex=2,即从第三个参数最先，都存入rest变量中，并作为第三个参数传入。第一二个参数稳固。
// example:_.without
// func.length=2，so startIndex=1,即从第二个参数最先，都存入rest变量中，并作为第二个参数传入第一个参数稳固。
// example:_.union
// func.length=1，so startIndex=0,行将一切参数都传入rest变量中，并作为第一个参数传入。
// 末了一种状况，func形参个数大于3，不再运用call手动传入参数
// 而是应用apply的数组参数特征，将参数保留在数组中，再传入函数。

var restArguments = function(func, startIndex) {
console.log('func2')
//func.length->形参个数
startIndex = startIndex == null ? func.length - 1 : +startIndex;
return function() { //func3
// arguments.length->实参个数
// 个人明白：此处arguments指的是最切近的这个闭包function在实行时传入的参数，并非func在实行时传入的参数个数。
console.log('func3')
var length = Math.max(arguments.length - startIndex, 0),
rest = Array(length),
index = 0;
for (; index rest[index] = arguments[index + startIndex];
}
switch (startIndex) {
case 0:
return func.call(this, rest);
case 1:
return func.call(this, arguments[0], rest);
case 2:
return func.call(this, arguments[0], arguments[1], rest);
}
var args = Array(startIndex + 1);
for (index = 0; index args[index] = arguments[index];
}
args[startIndex] = rest;
return func.apply(this, args);
};
};


// Invoke a method (with arguments) on every item in a collection.
// 在鸠合的每一个元素上挪用要领path，参数为arguments
// _.invoke([[3,4,5],[65,33,3]],&＃8217;sort&＃8217;)函数运转递次
// 在underscore.js加载编译时，restArgument被实行，console func2。并返回匿名函数func3
// 在_.invoke()被实行，即匿名函数func3被实行，console func3。此时的arguments=[[[3,4,5],[65,33,3]],&＃8217;sort&＃8217;]。返回匿名函数func实行的值
// 实行func，console func。参数obj = arguments[0]=[[[3,4,5],[65,33,3]],path = arguemnts[1]=&＃8217;sort&＃8217;,args = rest = []
// console func4
// console func4

_.invoke = restArguments(function(obj, path, args) { //func
console.log('func')
var contextPath, func;
if (_.isFunction(path)) {
func = path;
} else if (_.isArray(path)) {
cOntextPath= path.slice(0, -1);
path = path[path.length - 1];
}
return _.map(obj, function(context) { //func4
console.log('func4')
var method = func;
if (!method) {
if (contextPath && contextPath.length) {
cOntext= deepGet(context, contextPath);
}
if (cOntext== null) return void 0;
method = context[path];
}
return method == null ? method : method.apply(context, args);
});
});


// An internal function for creating a new object that inherits from another.

var baseCreate = function(prototype) {
if (!_.isObject(prototype)) return {};
if (nativeCreate) return nativeCreate(prototype);
Ctor.prototype = prototype;
var result = new Ctor;
Ctor.prototype = null;
return result;
};


// 偏函数与柯里函数区分
// 偏函数：传入某些牢固参数后，返回包括牢固参数，并可传入其他参数的函数
// 柯里函数：将n元参数的函数转变成n次函数，每次都只能传入一个参数。
// 接见属性函数

var shallowProperty = function(key) {
return function(obj) {
return obj == null ? void 0 : obj[key];
};
};


//推断是不是存在自有属性path

var has = function(obj, path) {
return obj != null && hasOwnProperty.call(obj, path);
}


//接见对象的深度多级属性 函数

var deepGet = function(obj, path) {
var length = path.length;
for (var i = 0; i if (obj == null) return void 0;
obj = obj[path[i]];
}
return length ? obj : void 0;
};


// Helper for collection methods to determine whether a collection
// should be iterated as an array or as an object.
// Related: http://people.mozilla.org/~jo&＃8230;
// Avoids a very nasty iOS 8 JIT bug on ARM-64. #2094
// js 最大的准确整数值

var MAX_ARRAY_INDEX = Math.pow(2, 53) - 1;
var getLength = shallowProperty('length');
var isArrayLike = function(collection) {
var length = getLength(collection);
return typeof length == 'number' && length >= 0 && length <= MAX_ARRAY_INDEX;
};


// Collection Functions
// &＃8212;&＃8212;&＃8212;&＃8212;&＃8212;&＃8212;&＃8211;
// The cornerstone, an each implementation, aka forEach.
// Handles raw objects in addition to array-likes. Treats all
// sparse array-likes as if they were dense.
// each与map区分
// each中iteratee函数实行效果不保留，返回obj自身
// map中iteratee函数实行效果保留到数组results中，并返回。

_.each = _.forEach = function(obj, iteratee, context) {
iteratee = optimizeCb(iteratee, context);
var i,
keys = !isArrayLike(obj) && _.keys(obj),
length = (keys || obj).length;
for (i = 0; i var currentKey = keys ? keys[i] : i;
iteratee(obj[currentKey], currentKey, obj);
}
return obj;
};


// Return the results of applying the iteratee to each element.

_.map = _.collect = function(obj, iteratee, context) {
//包装实行函数上下文
iteratee = cb(iteratee, context);
var keys = !isArrayLike(obj) && _.keys(obj),
length = (keys || obj).length,
results = Array(length);
for (var index = 0; index var currentKey = keys ? keys[index] : index;
results[index] = iteratee(obj[currentKey], currentKey, obj);
}
return results;
};


// Create a reducing function iterating left or right.
// 建立迭代函数，可选遍历方向

var createReduce = function(dir) {
// Wrap code that reassigns argument variables in a separate function than
// the one that accesses `arguments.length` to avoid a perf hit. (#1991)
// perf hit是performance hit的简写。
// arguments的运用，会致使一些机能题目。如chrome nodejs的v8引擎在运用arguments会代码优化步骤被跳过。
var reducer = function(obj, iteratee, memo, initial) { //func2
var keys = !isArrayLike(obj) && _.keys(obj),
length = (keys || obj).length,
index = dir > 0 ? 0 : length - 1;
if (!initial) {
memo = obj[keys ? keys[index] : index];
index += dir;
}
for (; index >= 0 && index var currentKey = keys ? keys[index] : index;
memo = iteratee(memo, obj[currentKey], currentKey, obj);
}
return memo;
};
// 此处返回func1函数，作用域中包括initial变量，存放了arguments.length，
// 意图就在于将arguments变量从reducer函数中分离出来，
// 并在挪用reducer函数时，开释argumenrs变量，防止机能题目。
return function(obj, iteratee, memo, context) { //func1
var initial = arguments.length >= 3;
return reducer(obj, optimizeCb(iteratee, context, 4), memo, initial);
};
};


// Reduce builds up a single result from a list of values, aka inject,
// or foldl.

_.reduce = _.foldl = _.inject = createReduce(1);


// The right-associative version of reduce, also known as foldr.

_.reduceRight = _.foldr = createReduce(-1);


// Return the first value which passes a truth test. Aliased as detect.
// 返回第一个断言问真的值

_.find = _.detect = function(obj, predicate, context) {
var keyFinder = isArrayLike(obj) ? _.findIndex : _.findKey;
var key = keyFinder(obj, predicate, context);
if (key !== void 0 && key !== -1) return obj[key];
};


// Return all the elements that pass a truth test.
// Aliased as select.
// 返回一切断言为真的值构成的数组，半途不中缀

_.filter = _.select = function(obj, predicate, context) {
var results = [];
predicate = cb(predicate, context);
_.each(obj, function(value, index, list) {
if (predicate(value, index, list)) results.push(value);
});
return results;
};


// Return all the elements for which a truth test fails.
// 返回一切断言为假的值，
// 内部直接挪用filter

_.reject = function(obj, predicate, context) {
return _.filter(obj, _.negate(cb(predicate)), context);
};


// Determine whether all of the elements match a truth test.
// Aliased as all.
// 推断是不是一切断言函数都为真，涌现假马上返回

_.every = _.all = function(obj, predicate, context) {
predicate = cb(predicate, context);
var keys = !isArrayLike(obj) && _.keys(obj),
length = (keys || obj).length;
for (var index = 0; index var currentKey = keys ? keys[index] : index;
if (!predicate(obj[currentKey], currentKey, obj)) return false;
}
return true;
};


// Determine if at least one element in the object matches a truth test.
// Aliased as any.
// 检测是不是至少有一个值断言为真，涌现真马上返回

_.some = _.any = function(obj, predicate, context) {
predicate = cb(predicate, context);
var keys = !isArrayLike(obj) && _.keys(obj),
length = (keys || obj).length;
for (var index = 0; index var currentKey = keys ? keys[index] : index;
if (predicate(obj[currentKey], currentKey, obj)) return true;
}
return false;
};


// Determine if the array or object contains a given item (using ===).
// Aliased as includes and include.
// 推断从fromIndex索引最先，是不是包括item

_.cOntains= _.includes = _.include = function(obj, item, fromIndex, guard) {
if (!isArrayLike(obj)) obj = _.values(obj);
if (typeof fromIndex != 'number' || guard) fromIndex = 0;
return _.indexOf(obj, item, fromIndex) >= 0;
};


// Convenience version of a common use case of map: fetching a property.
// 萃取数组对象中某属性值，返回一个数组

_.pluck = function(obj, key) {
return _.map(obj, _.property(key));
};


// Convenience version of a common use case of filter: selecting only objects
// containing specific key:value pairs.
// 遍历list中的每一个值，返回一个数组，这个数组里的元素包括 properties 所列出的键 &＃8211; 值对。

_.where = function(obj, attrs) {
return _.filter(obj, _.matcher(attrs));
};


// Convenience version of a common use case of find: getting the first object
// containing specific key:value pairs.
// 遍历全部list，返回 matches（婚配） properties参数所列出的一切 键 &＃8211; 值 对的第一个值。

_.findWhere = function(obj, attrs) {
return _.find(obj, _.matcher(attrs));
};


// Return the maximum element (or element-based computation).
// 返回list中的最大值。假如通报iteratee参数，iteratee将作为list中每一个值的排序依据。
// 假如list为空，将返回-Infinity，所以你能够须要事先用isEmpty搜检 list 。

_.max = function(obj, iteratee, context) {
var result = -Infinity,
lastComputed = -Infinity,
value, computed;
if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
obj = isArrayLike(obj) ? obj : _.values(obj);
for (var i = 0, length = obj.length; i value = obj[i];
if (value != null && value > result) {
result = value;
}
}
} else {
iteratee = cb(iteratee, context);
_.each(obj, function(v, index, list) {
computed = iteratee(v, index, list);
if (computed > lastComputed || computed === -Infinity && result === -Infinity) {
result = v;
lastComputed = computed;
}
});
}
return result;
};


// Return the minimum element (or element-based computation).
// 返回list中的最小值。假如通报iteratee参数，iteratee将作为list中每一个值的排序依据。
// 假如list为空，将返回Infinity，所以你能够须要事先用isEmpty搜检 list 。

_.min = function(obj, iteratee, context) {
var result = Infinity,
lastComputed = Infinity,
value, computed;
if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) {
obj = isArrayLike(obj) ? obj : _.values(obj);
for (var i = 0, length = obj.length; i value = obj[i];
if (value != null && value result = value;
}
}
} else {
iteratee = cb(iteratee, context);
_.each(obj, function(v, index, list) {
computed = iteratee(v, index, list);
if (computed result = v;
lastComputed = computed;
}
});
}
return result;
};


// Shuffle a collection.

_.shuffle = function(obj) {
return _.sample(obj, Infinity);
};


// Sample n random values from a collection using the modern version of the
// Fisher-Yates shuffle.
// If n is not specified, returns a single random element.
// The internal guard argument allows it to work with map.
// 从 list中发生一个随机样本。通报一个数字示意从list中返回n个随机元素。否则将返回一个单一的随机项。

_.sample = function(obj, n, guard) {
if (n == null || guard) {
if (!isArrayLike(obj)) obj = _.values(obj);
return obj[_.random(obj.length - 1)];
}
var sample = isArrayLike(obj) ? _.clone(obj) : _.values(obj);
var length = getLength(sample);
//取一个相符0-length的合理值
n = Math.max(Math.min(n, length), 0);
var last = length - 1;
for (var index = 0; index var rand = _.random(index, last);
var temp = sample[index];
sample[index] = sample[rand];
sample[rand] = temp;
}
return sample.slice(0, n);
};


// Sort the object&＃8217;s values by a criterion produced by an iteratee.
// 返回一个（稳固的）排序后的list拷贝副本。
// 假如通报iteratee参数，iteratee将作为list中每一个值的排序依据。
// 用来举行排序迭代器也能够是属性称号的字符串(比方 length)。

_.sortBy = function(obj, iteratee, context) {
var index = 0;
iteratee = cb(iteratee, context);
return _.pluck(_.map(obj, function(value, key, list) {
return {
value: value,
index: index++,
criteria: iteratee(value, key, list)
};
}).sort(function(left, right) {
var a = left.criteria;
var b = right.criteria;
if (a !== b) {
if (a > b || a === void 0) return 1;
if (a }
return left.index - right.index;
}), 'value');
};


// An internal function used for aggregate &＃8220;group by&＃8221; operations.
// 对鸠合每一个元素挪用iteratee函数后，获得key。
// 然后再依据behavior举行分组

var group = function(behavior, partition) {
return function(obj, iteratee, context) {
var result = partition ? [
[],
[]
] : {};
iteratee = cb(iteratee, context);
_.each(obj, function(value, index) {
var key = iteratee(value, index, obj);
behavior(result, value, key);
});
return result;
};
};


// Groups the object&＃8217;s values by a criterion. Pass either a string attribute
// to group by, or a function that returns the criterion.
// 把一个鸠合分组为多个鸠合，经由过程 iterator 返回的效果举行分组.
// 假如 iterator 是一个字符串而不是函数, 那末将运用 iterator 作为各元素的属性名来对照举行分组。

_.groupBy = group(function(result, value, key) {
if (has(result, key)) result[key].push(value);
else result[key] = [value];
});


// Indexes the object&＃8217;s values by a criterion, similar to groupBy, but for
// when you know that your index values will be unique.
// 给定一个list，和 一个用来返回一个在列表中的每一个元素键 的iterator 函数（或属性名）， 返回一个每一项索引的对象。
// 和groupBy异常像，然则当你晓得你的键是唯一的时刻能够运用indexBy 。

_.indexBy = group(function(result, value, key) {
result[key] = value;
});


// Counts instances of an object that group by a certain criterion. Pass
// either a string attribute to count by, or a function that returns the
// criterion.
// 排序一个列表构成多个组，而且返回各组中的对象的数量的计数。
// 相似groupBy，然则不是返回列表的值，而是返回在该组中值的数量。

_.countBy = group(function(result, value, key) {
if (has(result, key)) result[key]++;
else result[key] = 1;
});


var reStrSymbol = /¹|ud800-udbff|[ud800-udfff]/g;
// Safely create a real, live array from anything iterable.

_.toArray = function(obj) {
if (!obj) return [];
if (_.isArray(obj)) return slice.call(obj);
if (_.isString(obj)) {
// Keep surrogate pair characters together
return obj.match(reStrSymbol);
}
if (isArrayLike(obj)) return _.map(obj, _.identity);
return _.values(obj);
};


// Return the number of elements in an object.

_.size = function(obj) {
if (obj == null) return 0;
return isArrayLike(obj) ? obj.length : _.keys(obj).length;
};


// Split a collection into two arrays: one whose elements all satisfy the given
// predicate, and one whose elements all do not satisfy the predicate.
// 将 list 拆分为两个数组：第一个数组其元素都满足predicate迭代函数， 而第二个的一切元素均不能满足predicate迭代函数。
// predicate 经由过程 iteratee 举行转换，以简化速记语法。

_.partition = group(function(result, value, pass) {
result[pass ? 0 : 1].push(value);
}, true);


1. ud800-udfff &＃x21a9;