properties - What does this line of javascript mean? -

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I hope to learn some things in retina.js Opened, but I've been stumped on the first line.

var root = (typeof export === 'undefined'? Window: export);

What does this line actually do?

forward down,

function retina () {} root.Retina = Retina;

How was the retinal property established without root before it was defined?

typeof is the operator, which is used on a variable, Which is not defined at all, will still give the result in the value 'undefined' . Expression: 

  (typeof export === 'undefined'? Window: export)

Checks whether export window (global object in the browser), and if this happens, then the result of export (exporting) A standard name for things [type] from module - see) As a result, the route is assigned.

If you were thinking about conditional operators, 

  var d = a? B: C;  

  is equal to or equal to var d; If (A) {D = B; } And {d = c; }

As root.Retina = Retina; For JavaScript, like all other properties in JavaScript, there is no need to declare it and there is no facility to declare it.


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