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Global To-StringJavaScript Corners - Part 9

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二03 | 时间 2017 | 作者 红领巾 ] 0人收藏点击收藏

(This is Part 9 in my series on javascript corner cases ).

Here’s another one.

In JavaScript, global variables are properties of the global object. By default, the global object is like any other, and inherits from the Object . prototype object. Object . prototype comes with a number of its own properties, such as the toString method. So, that means that toString is also a global variable.

'use strict'; console.log(toString === global.toString); // prints "true" console.log(global.toString()); // prints "[object global]" console.log(toString()); // prints "[object Undefined]". Why is this?

This might seem a little confusing. The toString ( ) call is clearly invoking a function using a reference to that function, where the base of the reference is the global object, right? (Take a look at mypostsonreferences). So surely toString ( ) and global . toString ( ) mean the same thing?

Wrong.

There’s a subtlety here. The unqualified toString reference actually has a base valuethat is the global environment, which “knows about” the global object, but is not exactly the global object. The base object for the global environment is actually always the value undefined . See here in the spec . This is why it prints "[object Undefined]" .

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tags: global,object,toString,prints,log,base,reference,The,console,This,Part
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