javascript closure - how come I refer to an undeclared variable -

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• javascript closures vs. anonymous functions 11 answers

try head around javascript closures new me.
have tutorial indicates use:

function warningmaker( obstacle ){   function doalert (obs) {     alert("beware! there have been "+obs+" sightings in cove today!");   };   return doalert; } 

but confused "obs". parameter 'obstacle' automatically passed obs ?

a better example perhaps might be:

function warningmaker( obstacle ){   return function (number,location) {     alert("beware! there have been " +            obstacle +            " sightings in cove today!\n" +           number + " " + obstacle +           "(s) spotted @ " +           location + "!"          );   }; } 

either example you've got missing lines or isn't proper example closure. better example (with simplified code) be

function warningmaker(obstacle){    return function() {       alert("look!" + obstacle);    } } 

what above is, when function getting returned, reference obstacle in function body creates closure in memory , used whenever called ,

warningmaker("messi")(); // "look! messi" warningmaker("cr7")(); // "look! cr7" 

note in above, function returned being called. (i mean, empty parentheses)