javascript - How do I check if a property exists in an object/dictionary? -

i'm iterating on array of words , trying stuff them in object literal can assign value of how many times words occur each word in literal/dictionary. problem need check make sure word hasn't been added literal. tried using in check if property exists in literal it's throwing error:

cannot use 'in' operator search 'we' in undefined

here's problematic function:

i commented line that's causing problem

function wordcountdict(filename) {    wordcount = {};    inputfile = fs.readfile( root + filename, 'utf8', function( error, data ) {         if(error) {          console.log('error: ', error)           return false;       }        var words = data.split(" ");       (i in words) {           if(words[i] in wordcount) {  // problem occurs             wordcount[words[i]]++;          } else {             wordcount[words[i]] = 1;          }          console.log(words[i]);       }     }); } 

i'm coming python , best/easiest way achieve this, javascript doesn't seem agree.

how in javascript?

declare wordcount local variable function. getting overwritten elsewhere:

function wordcountdict(filename) {     var wordcount = {};     ... }