Javascript type of custom object

Question

How can I check if my javascript object is of a certain type.

var SomeObject = function() { } var s1 = new SomeObject(); 

In the case above typeof s1 will return "object". That's not very helpful. Is there some way to check if s1 is of type SomeObject ?

Answer 1

Yes, using instanceof (MDN link | spec link):

if (s1 instanceof SomeObject) { ... } 

Answer 2

Whatever you do, avoid obj.constructor.name or any string version of the constructor. That works great until you uglify/minify your code, then it all breaks since the constructor gets renamed to something obscure (ex: 'n') and your code will still do this and never match:

// Note: when uglified, the constructor may be renamed to 'n' (or whatever), // which breaks this code since the strings are left alone. if (obj.constructor.name === 'SomeObject') {} 

Note:

// Even if uglified/minified, this will work since SomeObject will // universally be changed to something like 'n'. if (obj instanceof SomeObject) {} 

(BTW, I need higher reputation to comment on the other worthy answers here)