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.

Answer 2

I didn't know that string is unchangeable unless your reassign it with new name

console.log(i, 'is a ' + typeof i);
var N = i.toUpperCase();
console.log(N);

Answer 3

var upperCase = string.toUpperCase();
console.log(upperCase);

toUpperCase doesn't transform existing string, it just returns a uppercase string.

Answer 4

.toUpperCase returns the upper-cased string. It is not an in-place modifier method.

string = string.toUpperCase();

Documentation: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/toUpperCase

Answer 5

String is Immutable. Once created, a string object can not be modified.

So here toUpperCase returns a new string, This should work-

var string ="kjsdgfiIJHBVSFIU";
var newString = string.toUpperCase();
alert(newString);

Answer 6

toUpperCase returns the new string, so you must write:

string = string.toUpperCase();

In many languages, strings are immutable, meaning that they can not be modified once created. While this costs in efficiency, it is important for object oriented programming, because if a String passed by reference to a function was modifiable, the state of objects could be changed without the object's consent.