YUI Array 之each| forEach(遍历）

1. yui-each原码：

YArray.each = YArray.forEach = Lang._isNative(Native.forEach) ? function (array, fn, thisObj) {
    Native.forEach.call(array || [], fn, thisObj || Y);
    return Y;
} : function (array, fn, thisObj) {
    for (var i = 0, len = (array && array.length) || 0; i < len; ++i) {
        if (i in array) {
            fn.call(thisObj || Y, array[i], i, array);
        }
    }

    return Y; //返回Y,便于链式操作
};

2.tangram-each

var T,baidu=T= function(){ 
///import baidu;
 
baidu.each = function( enumerable, iterator, context ) {
    var i, n, t, result;
 
    if ( typeof iterator == "function" && enumerable) {
 
        // Array or ArrayLike or NodeList or String or ArrayBuffer
        n = typeof enumerable.length == "number" ? enumerable.length : enumerable.byteLength;
        if ( typeof n == "number" ) {
 
            // 20121030 function.length
            //safari5.1.7 can not use typeof to check nodeList - linlingyu
            if (Object.prototype.toString.call(enumerable) === "[object Function]") {
                return enumerable;
            }
 
            for ( i=0; i<n; i++ ) {
                //enumerable[ i ] 有可能会是0
                t = enumerable[ i ];
                t === undefined && (t = enumerable.charAt && enumerable.charAt( i ));
                // 被循环执行的函数，默认会传入三个参数(i, array[i], array)
                result = iterator.call( context || t, i, t, enumerable );
 
                // 被循环执行的函数的返回值若为 false 和"break"时可以影响each方法的流程
                if ( result === false || result == "break" ) {break;}
            }
         
        // enumerable is number
        } else if (typeof enumerable == "number") {
 
            for (i=0; i<enumerable; i++) {
                result = iterator.call( context || i, i, i, i);
                if ( result === false || result == "break" ) { break;}
            }
         
        // enumerable is json
        } else if (typeof enumerable == "object") {
 
            for (i in enumerable) {
                if ( enumerable.hasOwnProperty(i) ) {
                    result = iterator.call( context || enumerable[ i ], i, enumerable[ i ], enumerable );
 
                    if ( result === false || result == "break" ) { break;}
                }
            }
        }
    }
 
    return enumerable;
};
 return baidu;
}();

3.tangram-array each原码

var T,baidu=T= function(){ 
///import baidu.type;
///import baidu.array;
///import baidu.each;
///import baidu.forEach;
 
baidu.array.extend({
    each: function(iterator, context){
        return baidu.each(this, iterator, context);
    },
     
    forEach: function(iterator, context){
        return baidu.forEach(this, iterator, context);
    }
});
/// Tangram 1.x Code Start
// TODO: delete in tangram 3.0
baidu.array.each = baidu.array.forEach = function(array, iterator, context) {
    var fn = function(index, item, array){
        return iterator.call(context || array, item, index, array);
    };
    return baidu.isEnumerable(array) ? baidu.each(array, typeof iterator == "function" ? fn : "", context) : array;
};
/// Tangram 1.x Code End
 return baidu;
}();

4.underscore  each 原码：

var each = _.each = _.forEach = function(obj, iterator, context) {
    if (obj == null) return;
    if (nativeForEach && obj.forEach === nativeForEach) {
      obj.forEach(iterator, context);
    } else if (obj.length === +obj.length) {
      for (var i = 0, l = obj.length; i < l; i++) {
        if (iterator.call(context, obj[i], i, obj) === breaker) return;
      }
    } else {
      for (var key in obj) {
        if (_.has(obj, key)) {
          if (iterator.call(context, obj[key], key, obj) === breaker) return;
        }
      }
    }
  };

5. qwrap – each 

forEach: function(arr, callback, pThis) {
			for (var i = 0, len = arr.length; i < len; i++) {
				if (i in arr) {
					callback.call(pThis, arr[i], i, arr);
				}
			}
		}

比较

  a. YUI会调用原生的forEach，可以用来遍历array,string，不能遍历object,也不会打断遍历

  b.tangram最严谨，排除了function具有length属性，但YUI与underscore用了in 这个来排除掉了function,可以返回break 或者false打断遍历，可以用来遍历对象

  c.  underscore 会调用原生的forEach，可以用来遍历对象，数组，字符串，可以被打断遍历，这个函数在underscore是一个基础的函数，

  d. qwrap的最简洁，不会调用原生forEach，也不能打断遍历