Produces a new array of values by mapping each value in?list?through a transformation function (iterator). If the native?map?method exists, it will be used instead. If?list?is a JavaScript object,?iterator's arguments will be?(value, key, list).

所有的javascript對象元素都將經過回調函數作用

1 _.map([1, 2, 3], function(num){ return num * 3; }); 2 => [3, 6, 9] 3 _.map({one : 1, two : 2, three : 3}, function(num, key){ return num * 3; }); 4 => [3, 6, 9]

源碼：

1 _.map = _.collect = function(obj, iterator, context) { 2 var results = []; 3 if (obj == null) return results; 4 if (nativeMap && obj.map === nativeMap) return obj.map(iterator, context); 5 each(obj, function(value, index, list) { 6 results[results.length] = iterator.call(context, value, index, list); 7 }); 8 if (obj.length === +obj.length) results.length = obj.length; 9 return results; 10 };

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轉載于:https://www.cnblogs.com/himan/archive/2012/04/20/2460726.html

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