The static String.fromCharCode() method returns a string created by using the specified sequence of Unicode values.

String.fromCharCode(num1[, ...[, numN]])

num1, ..., numN

A sequence of numbers that are Unicode values.

MDN link | MSDN link

This method returns a string and not a String object.

Because fromCharCode() is a static method of String, you always use it as String.fromCharCode(), rather than as a method of a String object you created.

String.fromCharCode(65, 66, 67);  // "ABC"

var test = String.fromCharCode(112, 108, 97, 105, 110);
document.write(test);

// Output: plain