lodash源码学习partial,partialRight

_.partial(func, [partials])

创建一个func的包装方法，调用这个方法可以提前传入部分func方法的参数.

这个方法感觉通常用在有很多参数相同的场景，然后将相同的参数提前传入、

比如

var ajax = (type,url,data,dataType,async) => {
    ..//具体实现
}
var ajGet = _.partial('get', _,  _, 'json', true)

ajGet('/user',{id:1})

来看看具体实现

//partial.js

var baseRest = require('./_baseRest'),//生成具有rest参数的方法
    createWrap = require('./_createWrap'),//函数包装方法
    getHolder = require('./_getHolder'),//得到占位符标识
    replaceHolders = require('./_replaceHolders');//替换占位符标识，并返回占位符索引的数组

var WRAP_PARTIAL_FLAG = 32;//partial标识

/**
 *    
 *
 *
 * @param {Function} func 需要包装的方法.
 * @param {...*} [partials] 提前传入的参数.
 * @returns {Function} 返回包装之后的方法.
 * @example
 *
 * function greet(greeting, name) {
 *   return greeting + ' ' + name;
 * }
 *
 * var sayHelloTo = _.partial(greet, 'hello');
 * sayHelloTo('fred');
 * // => 'hello fred'
 *
 * // Partially applied with placeholders.
 * var greetFred = _.partial(greet, _, 'fred');
 * greetFred('hi');
 * // => 'hi fred'
 */
var partial = baseRest(function(func, partials) {//处理partials，支持rest写法
  var holders = replaceHolders(partials, getHolder(partial));//得到占位符索引
  return createWrap(func, WRAP_PARTIAL_FLAG, undefined, partials, holders);//调用createWrap方法
});

// Assign default placeholders.
partial.placeholder = {};

module.exports = partial;

这个方法同样依赖于createWrap方法

//_createWrap.js

var baseSetData = require('./_baseSetData'),
    createBind = require('./_createBind'),
    createCurry = require('./_createCurry'),
    createHybrid = require('./_createHybrid'),
    createPartial = require('./_createPartial'),//创建部分参数方法
    getData = require('./_getData'),
    mergeData = require('./_mergeData'),
    setData = require('./_setData'),
    setWrapToString = require('./_setWrapToString'),
    toInteger = require('./toInteger');

var FUNC_ERROR_TEXT = 'Expected a function';

//各种方法的位掩码标识
var WRAP_BIND_FLAG = 1,
    WRAP_BIND_KEY_FLAG = 2,
    WRAP_CURRY_FLAG = 8,
    WRAP_CURRY_RIGHT_FLAG = 16,
    WRAP_PARTIAL_FLAG = 32,
    WRAP_PARTIAL_RIGHT_FLAG = 64;

var nativeMax = Math.max;//原生最大值方法

/**
 * 创建一个函数，该函数可以创建或调用func用可选的this和部分应用的参数.
 *
 * @param {Function|string} func 需要包装的函数.
 * @param {number} bitmask 位掩码标识
 * @param {*} [thisArg] func的this对象
 * @param {Array} [partials] 应用的参数
 * @param {Array} [holders] 占位符的索引
 * @param {Array} [argPos] .
 * @param {number} [ary] .
 * @param {number} [arity] 可用参数数量.
 * @returns {Function} 返回包装之后的函数.
 */
 //lodash使用BitMask来进行各种方法的表示，BitMask使用方法可以看 http://geek.csdn.net/news/detail/73343

function createWrap(func, bitmask, thisArg, partials, holders, argPos, ary, arity) {
  var isBindKey = bitmask & WRAP_BIND_KEY_FLAG;
  if (!isBindKey && typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  var length = partials ? partials.length : 0;//传入的参数个数，不传为0
  if (!length) {//如果没有传入partials
    bitmask &= ~(WRAP_PARTIAL_FLAG | WRAP_PARTIAL_RIGHT_FLAG);//清除WRAP_PARTIAL_FLAG和WRAP_PARTIAL_RIGHT_FLAG
    partials = holders = undefined;//部分参数和占位符索引都为undefined
  }
  ary = ary === undefined ? ary : nativeMax(toInteger(ary), 0);
  arity = arity === undefined ? arity : toInteger(arity);
  length -= holders ? holders.length : 0;//如果有占位符，参数长度减去占位符长度

  if (bitmask & WRAP_PARTIAL_RIGHT_FLAG) {//是否是WRAP_PARTIAL_RIGHT_FLAG(不是，跳过)
    var partialsRight = partials,
        holdersRight = holders;

    partials = holders = undefined;
  }
  var data = isBindKey ? undefined : getData(func);

  var newData = [
    func, bitmask, thisArg, partials, holders, partialsRight, holdersRight,
    argPos, ary, arity
  ];//将所有参数赋值给newData

  if (data) {
    mergeData(newData, data);
  }
  func = newData[0];
  bitmask = newData[1];
  thisArg = newData[2];
  partials = newData[3];
  holders = newData[4];
  arity = newData[9] = newData[9] === undefined
    ? (isBindKey ? 0 : func.length)
    : nativeMax(newData[9] - length, 0);

  if (!arity && bitmask & (WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG)) {
    bitmask &= ~(WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG);
  }
  if (!bitmask || bitmask == WRAP_BIND_FLAG) {//
    var result = createBind(func, bitmask, thisArg);
  } else if (bitmask == WRAP_CURRY_FLAG || bitmask == WRAP_CURRY_RIGHT_FLAG) {
    result = createCurry(func, bitmask, arity);
  } else if ((bitmask == WRAP_PARTIAL_FLAG || bitmask == (WRAP_BIND_FLAG | WRAP_PARTIAL_FLAG)) && !holders.length) {
    result = createPartial(func, bitmask, thisArg, partials);//如果没有占位符，调用createPartial方法
  } else {
    result = createHybrid.apply(undefined, newData);//否则调用createHybrid
  }
  var setter = data ? baseSetData : setData;//设置data的元数据（暂不分析）
  return setWrapToString(setter(result, newData), func, bitmask);//给包装之后的方法添加元数据（用于优化），添加toStirng方法，并返回func(具体实现暂不分析)
}

module.exports = createWrap;

依赖的createPartial方法

//_createPartial.js

var apply = require('./_apply'),//同Function.apply
    createCtor = require('./_createCtor'),//创建一个可以创建函数实例的方法
    root = require('./_root');//根元素

var WRAP_BIND_FLAG = 1;//bind方法位掩码

/**
 * 创建一个func的包装方法，调用这个方法可以使用可选的this对象和提前传入部分参数.
 *
 * @private
 * @param {Function} func 需要包装的方法.
 * @param {number} 位掩码标识.
 * @param {*} thisArg func的this对象.
 * @param {Array} partials 提前传入的参数.
 * @returns {Function} 返回新的包装方法.
 */
function createPartial(func, bitmask, thisArg, partials) {
  var isBind = bitmask & WRAP_BIND_FLAG,//是否是bind方法
      Ctor = createCtor(func);//用于创建实例的构造器

  function wrapper() {
    var argsIndex = -1,//参数索引
        argsLength = arguments.length,//传入参数个数
        leftIndex = -1,//提前传入参数索引
        leftLength = partials.length,//提前传入参数个数
        args = Array(leftLength + argsLength),//总参数
        fn = (this && this !== root && this instanceof wrapper) ? Ctor : func;//如果是根元素调用，使用func，否则使用Ctor

    while (++leftIndex < leftLength) {//遍历partials,将参数作为调用方法的前面的参数
      args[leftIndex] = partials[leftIndex];
    }
    while (argsLength--) {//遍历传入的参数，将其作为调用方法的后面的参数
      args[leftIndex++] = arguments[++argsIndex];
    }
    return apply(fn, isBind ? thisArg : this, args);//调用fn,传入this对象和参数
  }
  return wrapper;//返回wrapper方法
}

module.exports = createPartial;

依赖的createHybrid方法

//_createHybrid.js

var composeArgs = require('./_composeArgs'),//组合参数方法
    composeArgsRight = require('./_composeArgsRight'),
    countHolders = require('./_countHolders'),
    createCtor = require('./_createCtor'),
    createRecurry = require('./_createRecurry'),
    getHolder = require('./_getHolder'),
    reorder = require('./_reorder'),
    replaceHolders = require('./_replaceHolders'),
    root = require('./_root');

//位掩码标识
var WRAP_BIND_FLAG = 1,
    WRAP_BIND_KEY_FLAG = 2,
    WRAP_CURRY_FLAG = 8,
    WRAP_CURRY_RIGHT_FLAG = 16,
    WRAP_ARY_FLAG = 128,
    WRAP_FLIP_FLAG = 512;

/**
 * 创建一个包装函数，调用func使用可选的thisArg，应用部分参数和柯里化.
 *
 * @param {Function|string} func 需要包装的方法.
 * @param {number} bitmask 位掩码标识
 * @param {*} [thisArg] this对象.
 * @param {Array} [partials] 实现传入的参数.
 * @param {Array} [holders] 占位符.
 * @param {Array} [partialsRight] .
 * @param {Array} [holdersRight] .
 * @param {Array} [argPos] .
 * @param {number} [ary] .
 * @param {number} [arity] 可用函数参数数量.
 * @returns {Function} 返回新的包装函数.
 */
function createHybrid(func, bitmask, thisArg, partials, holders, partialsRight, holdersRight, argPos, ary, arity) {
  var isAry = bitmask & WRAP_ARY_FLAG,
      isBind = bitmask & WRAP_BIND_FLAG,
      isBindKey = bitmask & WRAP_BIND_KEY_FLAG,
      isCurried = bitmask & (WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG),
      isFlip = bitmask & WRAP_FLIP_FLAG,
      Ctor = isBindKey ? undefined : createCtor(func);

  function wrapper() {
    var length = arguments.length,//参数个数
        args = Array(length),//保存所有参数
        index = length;//参数数组索引

    while (index--) {//遍历参数，将所有参数存入args
      args[index] = arguments[index];
    }
    if (isCurried) {
      var placeholder = getHolder(wrapper),
          holdersCount = countHolders(args, placeholder);
    }
    if (partials) {//执行composeArgs，对参数进行组合
      args = composeArgs(args, partials, holders, isCurried);
    }
    if (partialsRight) {
      args = composeArgsRight(args, partialsRight, holdersRight, isCurried);
    }
    length -= holdersCount;//参数个数减去占位符数量
    if (isCurried && length < arity) {
      var newHolders = replaceHolders(args, placeholder);
      return createRecurry(
        func, bitmask, createHybrid, wrapper.placeholder, thisArg,
        args, newHolders, argPos, ary, arity - length
      );
    }
    var thisBinding = isBind ? thisArg : this,
        fn = isBindKey ? thisBinding[func] : func;

    length = args.length;//参数长度
    if (argPos) {
      args = reorder(args, argPos);
    } else if (isFlip && length > 1) {
      args.reverse();
    }
    if (isAry && ary < length) {
      args.length = ary;
    }
    if (this && this !== root && this instanceof wrapper) {
      fn = Ctor || createCtor(fn);
    }
    return fn.apply(thisBinding, args);//调用fn，并且传入args
  }
  return wrapper;//返回包装方法
}
module.exports = createHybrid;

依赖的composeArgs方法

//composeArgs.js

var nativeMax = Math.max;//原生求最大值方法

/**
 * 创建一个由提前传入的参数，占位符和传入的参数组成的一维数组.
 *
 * @private
 * @param {Array} args 提供的参数.
 * @param {Array} partials 提前传入的参数.
 * @param {Array} holders 提前传入参数中的占位符索引.
 * @params {boolean} [isCurried] 指定是否组成一个柯里化函数.
 * @returns {Array} 返回新的参数集合.
 */
function composeArgs(args, partials, holders, isCurried) {
  var argsIndex = -1,//传入参数索引
      argsLength = args.length,//参数个数
      holdersLength = holders.length,//占位符个数
      leftIndex = -1,//提前传入参数索引
      leftLength = partials.length,//提前传入参数个数
      rangeLength = nativeMax(argsLength - holdersLength, 0),//实际参数个数
      result = Array(leftLength + rangeLength),//返回结果数组
      isUncurried = !isCurried;//是否并未柯里化

  while (++leftIndex < leftLength) {//遍历partials，将其传入result
    result[leftIndex] = partials[leftIndex];
  }
  while (++argsIndex < holdersLength) {//遍历holders,将result中对应索引的值，换成传入的参数对应的值
    if (isUncurried || argsIndex < argsLength) {
      result[holders[argsIndex]] = args[argsIndex];
    }
  }
  while (rangeLength--) {//遍历args，将剩余的参数传入reslut
    result[leftIndex++] = args[argsIndex++];
  }
  return result;//返回生产的完整参数数组
}

module.exports = composeArgs;

_.partialRight(func, [partials])

和_.partial很像，只不过提前传入的参数是func从末尾开始的参数

这个方法的使用场景和partial差不多，就不分析了，直接看具体实现

//partialRight.js

var baseRest = require('./_baseRest'),//生成具有rest参数的方法
    createWrap = require('./_createWrap'),//函数包装方法
    getHolder = require('./_getHolder'),//得到占位符标识
    replaceHolders = require('./_replaceHolders');//替换占位符标识，并返回占位符索引的数组

var WRAP_PARTIAL_RIGHT_FLAG = 64;//partialRight位掩码标识

/**
 * 
 *
 * @param {Function} func 需要包装的方法.
 * @param {...*} [partials] 提前传入的参数.
 * @returns {Function} 返回包装之后的方法.
 * @example
 *
 * function greet(greeting, name) {
 *   return greeting + ' ' + name;
 * }
 *
 * var greetFred = _.partialRight(greet, 'fred');
 * greetFred('hi');
 * // => 'hi fred'
 *
 * // Partially applied with placeholders.
 * var sayHelloTo = _.partialRight(greet, 'hello', _);
 * sayHelloTo('fred');
 * // => 'hello fred'
 */
var partialRight = baseRest(function(func, partials) {//处理partials，支持rest写法
  var holders = replaceHolders(partials, getHolder(partialRight));//得到占位符索引
  return createWrap(func, WRAP_PARTIAL_RIGHT_FLAG, undefined, partials, holders);//调用createWrap方法
});

// Assign default placeholders.
partialRight.placeholder = {};

module.exports = partialRight;

基本上实现都和partial一样

//_createWrap.js

var baseSetData = require('./_baseSetData'),
    createBind = require('./_createBind'),
    createCurry = require('./_createCurry'),
    createHybrid = require('./_createHybrid'),
    createPartial = require('./_createPartial'),//创建部分参数方法
    getData = require('./_getData'),
    mergeData = require('./_mergeData'),
    setData = require('./_setData'),
    setWrapToString = require('./_setWrapToString'),
    toInteger = require('./toInteger');

var FUNC_ERROR_TEXT = 'Expected a function';

//各种方法的位掩码标识
var WRAP_BIND_FLAG = 1,
    WRAP_BIND_KEY_FLAG = 2,
    WRAP_CURRY_FLAG = 8,
    WRAP_CURRY_RIGHT_FLAG = 16,
    WRAP_PARTIAL_FLAG = 32,
    WRAP_PARTIAL_RIGHT_FLAG = 64;

var nativeMax = Math.max;//原生最大值方法

/**
 * 创建一个函数，该函数可以创建或调用func用可选的this和部分应用的参数.
 *
 * @param {Function|string} func 需要包装的函数.
 * @param {number} bitmask 位掩码标识
 * @param {*} [thisArg] func的this对象
 * @param {Array} [partials] 应用的参数
 * @param {Array} [holders] 占位符的索引
 * @param {Array} [argPos] .
 * @param {number} [ary] .
 * @param {number} [arity] 可用参数数量.
 * @returns {Function} 返回包装之后的函数.
 */
 //lodash使用BitMask来进行各种方法的表示，BitMask使用方法可以看 http://geek.csdn.net/news/detail/73343

function createWrap(func, bitmask, thisArg, partials, holders, argPos, ary, arity) {
  var isBindKey = bitmask & WRAP_BIND_KEY_FLAG;
  if (!isBindKey && typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  var length = partials ? partials.length : 0;//传入的参数个数，不传为0
  if (!length) {//如果没有传入partials
    bitmask &= ~(WRAP_PARTIAL_FLAG | WRAP_PARTIAL_RIGHT_FLAG);//清除WRAP_PARTIAL_FLAG和WRAP_PARTIAL_RIGHT_FLAG
    partials = holders = undefined;//部分参数和占位符索引都为undefined
  }
  ary = ary === undefined ? ary : nativeMax(toInteger(ary), 0);
  arity = arity === undefined ? arity : toInteger(arity);
  length -= holders ? holders.length : 0;//如果有占位符，参数长度减去占位符长度

  if (bitmask & WRAP_PARTIAL_RIGHT_FLAG) {//是否是WRAP_PARTIAL_RIGHT_FLAG(是的)
    var partialsRight = partials,
        holdersRight = holders;

    partials = holders = undefined;
  }
  var data = isBindKey ? undefined : getData(func);

  var newData = [
    func, bitmask, thisArg, partials, holders, partialsRight, holdersRight,
    argPos, ary, arity
  ];//将所有参数赋值给newData

  if (data) {
    mergeData(newData, data);
  }
  func = newData[0];
  bitmask = newData[1];
  thisArg = newData[2];
  partials = newData[3];
  holders = newData[4];
  arity = newData[9] = newData[9] === undefined
    ? (isBindKey ? 0 : func.length)
    : nativeMax(newData[9] - length, 0);

  if (!arity && bitmask & (WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG)) {
    bitmask &= ~(WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG);
  }
  if (!bitmask || bitmask == WRAP_BIND_FLAG) {//
    var result = createBind(func, bitmask, thisArg);
  } else if (bitmask == WRAP_CURRY_FLAG || bitmask == WRAP_CURRY_RIGHT_FLAG) {
    result = createCurry(func, bitmask, arity);
  } else if ((bitmask == WRAP_PARTIAL_FLAG || bitmask == (WRAP_BIND_FLAG | WRAP_PARTIAL_FLAG)) && !holders.length) {
    result = createPartial(func, bitmask, thisArg, partials);
  } else {
    result = createHybrid.apply(undefined, newData);//否则调用createHybrid
  }
  var setter = data ? baseSetData : setData;//设置data的元数据（暂不分析）
  return setWrapToString(setter(result, newData), func, bitmask);//给包装之后的方法添加元数据（用于优化），添加toStirng方法，并返回func(具体实现暂不分析)
}

module.exports = createWrap;

createHybrid

//_createHybrid.js

var composeArgs = require('./_composeArgs'),//组合参数方法
    composeArgsRight = require('./_composeArgsRight'),
    countHolders = require('./_countHolders'),
    createCtor = require('./_createCtor'),
    createRecurry = require('./_createRecurry'),
    getHolder = require('./_getHolder'),
    reorder = require('./_reorder'),
    replaceHolders = require('./_replaceHolders'),
    root = require('./_root');

//位掩码标识
var WRAP_BIND_FLAG = 1,
    WRAP_BIND_KEY_FLAG = 2,
    WRAP_CURRY_FLAG = 8,
    WRAP_CURRY_RIGHT_FLAG = 16,
    WRAP_ARY_FLAG = 128,
    WRAP_FLIP_FLAG = 512;

/**
 * 创建一个包装函数，调用func使用可选的thisArg，应用部分参数和柯里化.
 *
 * @param {Function|string} func 需要包装的方法.
 * @param {number} bitmask 位掩码标识
 * @param {*} [thisArg] this对象.
 * @param {Array} [partials] 实现传入的参数.
 * @param {Array} [holders] 占位符.
 * @param {Array} [partialsRight] .
 * @param {Array} [holdersRight] .
 * @param {Array} [argPos] .
 * @param {number} [ary] .
 * @param {number} [arity] 可用函数参数数量.
 * @returns {Function} 返回新的包装函数.
 */
function createHybrid(func, bitmask, thisArg, partials, holders, partialsRight, holdersRight, argPos, ary, arity) {
  var isAry = bitmask & WRAP_ARY_FLAG,
      isBind = bitmask & WRAP_BIND_FLAG,
      isBindKey = bitmask & WRAP_BIND_KEY_FLAG,
      isCurried = bitmask & (WRAP_CURRY_FLAG | WRAP_CURRY_RIGHT_FLAG),
      isFlip = bitmask & WRAP_FLIP_FLAG,
      Ctor = isBindKey ? undefined : createCtor(func);

  function wrapper() {
    var length = arguments.length,//参数个数
        args = Array(length),//保存所有参数
        index = length;//参数数组索引

    while (index--) {//遍历参数，将所有参数存入args
      args[index] = arguments[index];
    }
    if (isCurried) {
      var placeholder = getHolder(wrapper),
          holdersCount = countHolders(args, placeholder);
    }
    if (partials) {
      args = composeArgs(args, partials, holders, isCurried);
    }
    if (partialsRight) {//执行composeArgsRight，对参数进行组合
      args = composeArgsRight(args, partialsRight, holdersRight, isCurried);
    }
    length -= holdersCount;//参数个数减去占位符数量
    if (isCurried && length < arity) {
      var newHolders = replaceHolders(args, placeholder);
      return createRecurry(
        func, bitmask, createHybrid, wrapper.placeholder, thisArg,
        args, newHolders, argPos, ary, arity - length
      );
    }
    var thisBinding = isBind ? thisArg : this,
        fn = isBindKey ? thisBinding[func] : func;

    length = args.length;//参数长度
    if (argPos) {
      args = reorder(args, argPos);
    } else if (isFlip && length > 1) {
      args.reverse();
    }
    if (isAry && ary < length) {
      args.length = ary;
    }
    if (this && this !== root && this instanceof wrapper) {
      fn = Ctor || createCtor(fn);
    }
    return fn.apply(thisBinding, args);//调用fn，并且传入args
  }
  return wrapper;//返回包装方法
}
module.exports = createHybrid;

composeArgsRight

//_composeArgsRight.js

var nativeMax = Math.max;//原生求最大值方法

/**
 * 和composeArgs很像，只是组合参数的方向相反
 *
* @private
 * @param {Array} args 提供的参数.
 * @param {Array} partials 提前传入的参数.
 * @param {Array} holders 提前传入参数中的占位符索引.
 * @params {boolean} [isCurried] 指定是否组成一个柯里化函数.
 * @returns {Array} 返回新的参数集合.
 */
function composeArgsRight(args, partials, holders, isCurried) {
  var argsIndex = -1,//参数索引
      argsLength = args.length,//传入参数个数
      holdersIndex = -1,//占位符索引
      holdersLength = holders.length,//占位符个数
      rightIndex = -1,//提前传入参数索引
      rightLength = partials.length,//提前传入参数个数
      rangeLength = nativeMax(argsLength - holdersLength, 0),//实际传入参数个数
      result = Array(rangeLength + rightLength),//结果参数数组
      isUncurried = !isCurried;

  while (++argsIndex < rangeLength) {//遍历传入参数，将其传入result
    result[argsIndex] = args[argsIndex];
  }
  var offset = argsIndex;
  while (++rightIndex < rightLength) {//遍历partials，将其传入result
    result[offset + rightIndex] = partials[rightIndex];
  }
  while (++holdersIndex < holdersLength) {//遍历占位符索引，将result中对应索引的值，换成传入的参数对应的值
    if (isUncurried || argsIndex < argsLength) {
      result[offset + holders[holdersIndex]] = args[argsIndex++];
    }
  }
  return result;//返回生成的完整参数数组
}

module.exports = composeArgsRight;