Improved typeof for the exact object type

When I first started writing scripts in Javascript, the typeof() operator did not capture much of my attention.

Because of my experience in other programming languages, I naturally believed that the operator would give me the exact name and this firm belief cost me many hours of debugging.

And when I realized that the operator won’t even tell me whether a given object is an instance of Array or Date, it was very frustrating because I’ve designed the entire script based on the assumption that the operator would provide me the exact object type.

So, I wrote the following short function, which privodes the constructor’s function name when it was given an object.

 * You can find more about this function at
 * Copyright (c) 2008 Andy G.P. Na <[email protected]>
 * The source code is freely distributable under the terms of an MIT-style license.
function getType(v){
 var result = typeof(v);
 if (result == "object"){
  result = "@unknown";
   var sConstructor = v.constructor.toString();
   var iStartIdx = sConstructor.indexOf(' ' ) + 1;
   var iLength = sConstructor.indexOf('(' ) - iStartIdx;

   var sFuncName = sConstructor.substr(iStartIdx, iLength);
   if (iStartIdx && sFuncName) result = sFuncName;
 return result.toLowerCase();

“@” was added in front of the word “unknown” because the function name can actually be “unknown” and this confusion can be avoided by adding “@”, which cannot be used for function names.


3 Replies to “Improved typeof for the exact object type”

  1. It would be nice to wrap the result in toLowerCase to have a value more similar to what native typeof would return.

    => ‘object’ //not ‘Object’

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