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javascriptobjectvarecmascript-5

Difference between window's properties and global variable

I try to run a code below in browser. I thought property window.a and global a is the same cell in memory. Could somebody please give me a link to an article which explains this behaviour.

// undefined
// if (window.a) {}

// Uncaught ReferenceError: a is not defined
// if (a) {}
Solution

  • They are the same:

    a = 1;
a === window.a // true

    Edit: Sorry, was a bit too quick there... I diddnt answer anything. This article explains the difference pretty well: https://javascriptweblog.wordpress.com/2010/08/16/understanding-undefined-and-preventing-referenceerrors/

    "A Reference is considered unresolvable if its base value is undefined"

    window.a // base value is window, reference object is a
a // base value is a