为什么require（'下划线'）在node.js REPL执行时返回undefined？ [英] Why does require('underscore') return undefined when executed at the node.js REPL?

问题描述

当我在控制台中运行节点并输入 var _ = require（'underscore'）; ， _ 最终未定义。如果我将相同的代码放在一个文件中并执行它，下划线库将按预期包含。

When I run node in my console and type var _ = require('underscore');, _ ends up undefined. If I put the same code in a file and execute it, the underscore library gets included as expected.

$ node
> var _ = require('underscore');
> console.log(_)
undefined // underscore library does not load
> var async = require('async');
undefined
> console.log(async) // async library does
{ noConflict: [Function],
  nextTick: [Function],
  forEach: [Function],
...
>

但.js文件中的相同代码作为节点test.js执行显示两个库按预期加载。发生了什么？

But the same code in a .js file executed as node test.js shows both libraries loading as expected. What's going on?

推荐答案

节点repl将 _ 绑定到值最后评估的输入;它会在 var _ = ...; 中覆盖 _ 绑定。另请参阅关于repl 的node.js文档。

The Node repl binds _ to the value of the last evaluated input; which overwrites your _ binding in var _ = ...;. Also see the node.js documentation on the repl.

无论是什么替换 ... ，都是如此：

This is true no matter what replaces ..., for example:

$ node
> var _ = "any value";
undefined
> _
undefined

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