javascript - Return from closure? -

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how 1 return closure, without returning containing function?

in following function, return statement returns gm_xmlhttprequest: not closure. naturally can see arrange code that execution drops off end of closure, i'm curious how return in example.

function gm_xmlhttprequest(details, callback) {   var xhr = new xmlhttprequest();   xhr.onreadystatechange = function() {     if (xhr.readystate != 4)       return; // <-- zomg returns parent function wtf     if (xhr.status != 200)       callback(null);     callback(xhr);   }   xhr.open('get', details.url, true);   xhr.send(); };

return ever exit callee (current function) , return control caller (calling "parent" function), never return caller. in situation describe, callee anonymous function set onreadystatechange , there no caller (per se).

gm_xmlhttprequest returns undefined after xhr.send() line before onreadystatechange function runs because there no return statement , xhr asynchronous. "zomg wtf" line exit anonymous function since there no caller pass control to.

from ecma-262, 3rd , 5th editions (section 12.9 return statement):

a return statement causes function cease execution , return value caller. if expression omitted, return value undefined. otherwise, return value value of expression.


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