toUpperCase() is not making the string upper case

Question

I don\'t know what I\'m doing wrong; But somehow .toUpperCase() String-function is not working on my browser or do I get something wrong?

var string          


        

Answer 1

Previous answers about Strings being immutable are great! Here is just another potential run-time reason for getting this error which might be hard to spot at first. It does not detract from any of the above valid answers:

If the object on which the .toUpperCase() method is invoked is not a String, then the runtime doesn't 'find' the method toUpperCase() since that method/function only exists on String objects.

e.g. console.log(variableName.toUpperCase());

If variableName is of the type String, it works fine. If it is of another type (that does not have a toUpperCase() method, it says 'toUpperCase() is not a function (since it isn't).

If you know it should be a string, you can cast it like this:

console.log(String(variableName).toUppercase());

Hope it helps.