理解_.js中下划线的声明吗？-前端问题

Understanding the declaration of the underscore in _.js?(理解_.js中下划线的声明吗？)

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问题描述

这是从annotated source of _.js开始的。尽管我可能会尝试，但我的JavaScript能力还不够高，无法理解这里发生的事情。我希望有人能一步一步地给出一个真实的解释。我真的不知道下面的代码除了以某种方式设置_以供使用之外还有什么作用，尽管我理解每个表达式。

var _ = function(obj) { if (obj instanceof _) return obj; if (!(this instanceof _)) return new _(obj); this._wrapped = obj; }; if (typeof exports !== 'undefined') { if (typeof module !== 'undefined' && module.exports) { exports = module.exports = _; } exports._ = _; } else { root._ = _; }

推荐答案
var _ = function(obj) { // Either serve as the identity function on `_` instances, // ... or instantiate a new `_` object for other input. // If an `_` instance was passed, return it. if (obj instanceof _) return obj; // If someone called `_(...)`, rather than `new _(...)`, // ... return `new _(...)` to instantiate an instance. if (!(this instanceof _)) return new _(obj); // If we are instantiating a new `_` object with an underlying, // ... object, set that object to the `_wrapped` property. this._wrapped = obj; }; // If there is an exports value (for modularity)... if (typeof exports !== 'undefined') { // If we're in Node.js with module.exports... if (typeof module !== 'undefined' && module.exports) { // Set the export to `_` exports = module.exports = _; } // Export `_` as `_` exports._ = _; } else { // Otherwise, set `_` on the global object, as set at the beginning // ... via `(function(){ var root = this; /* ... */ }())` root._ = _; }

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