javascript - node.js array check fails conditional is processed even while returning false -

i have buffer in node.js , i'm checking mime type regex.
there capturing group in regex , if successfull must return capturing group @ index 1 in array returned exec.

i'm using

if(mime.exec(dt)[1]){     tip.push(mime.exec(dt)[1]); } 

this control , tried

if(1 in mime.exec) 

and

mime.exec.hasownproperty(1) 

but anyway condition processed , gives traceback

typeerror: cannot  read property '1' of null 

what kind of mechanism can use fix issue?

update ----

var mime=/^content-type: (.+\s)/igm;

update ----

var fs = require("fs"),     mime = /^content-type: (.+\s)/igm,     tip = []; require("http").createserver(function(req, res) {     var data = "";     console.log("working...");     console.log(req.method);     if (req.method.touppercase() == "post") {          req.once("data", function() {             fs.writefilesync("dene.txt", "");         });         req.on("data", function(dt) {             fs.appendfilesync("dene.txt", dt.tostring("utf8"));             if (mime.exec(dt)[1]) {                 tip.push(mime.exec(dt)[1]);             } else {                 return false;             }          });          req.on("end", function() {             console.log(((fs.statsync("dene.txt").size) / 1024).tofixed(2), "kb");             console.log(tip);          });     }     res.writehead(200, {         "content-type": "text/html"     });     res.end(require("fs").readfilesync(require("path").resolve(__dirname, "static_files/post.html"))); }).listen(3000) 

change this

if (mime.exec(dt)[1]) { 

to this

if (mime.exec(dt) && mime.exec(dt)[1]) { 

exec returns either null or array -- test null first because can't treat null array.

edit: mentioned in comments, there additional considerations keep in mind if using global regex.

so, global regexes, super-safe version:

var rslt = mime.exec(dt) if (rslt && rslt[1]) {   tip.push(rslt[1]);