The "String" Object Type - Not Equal to String Primitive Type

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∟The "String" Object Type - Not Equal to String Primitive Type

This section provides a quick description and a tutorial example script on the 'String' built-in object type, which is used to create 'String' objects. Watch out: 'String' objects are not string values.

The "String" object type is a special built-in object type to be used to create a "String" object, which is different than a string value of the string primitive type. It has the following main features:

New "String" objects can be created with the "String()" constructor. Note that "String()" is also a regular function, which returns a string value, not a "String" object.
All "String" objects have an inherited property called "length" representing the number of characters of the string.
All "String objects have many inherited methods: toString(), charAt(), charCodeAt(), concat(), indexOf(), etc.. Accessing those inherited methods is the main reason of using "String" objects instead of string values.
A string literal, "...", creates a string value, not a "String" object.
A string value can be converted to a "String" object on the fly with the (.) operator, for example: "string".length.

Here is a tutorial example script showing some of those features:

// String_Object_Type.js
// Copyright (c) 2013 HerongYang.com. All Rights Reserved.

   // Creating a new String object
   var message = new String("Hello World!");

   // Checking this object
   println("\nAbout this \"message\":");
   println("   Type = "+(typeof message));
   println("   Instance Of Object: "+(message instanceof Object));
   println("   Instance Of String: "+(message instanceof String));
   
   // Using String's inherited property and method
   var upperMessage = message.toUpperCase();
   var l = message.length;
   var subMessage = message.substring(0,l-7);

   println("\nExecution result:");
   println("   typeof message = "+(typeof message));
   println("   message.toString() = "+message.toString());
   println("   typeof upperMessage = "+(typeof upperMessage));
   println("   upperMessage = "+upperMessage);
   println("   typeof subMessage = "+(typeof subMessage));
   println("   subMessage = "+subMessage);

   println("\nConverting to String objects on the fly:");
   println("   \"...\".length = "+("Hello World!".length));
   println("   \"...\".toUpperCase() = "
      +("Hello World!".toUpperCase()));

If you run this script with "jrunscript", you will get:

About this "message":
   Type = object
   Instance Of Object: true
   Instance Of String: true

Execution result:
   typeof message = object
   message.toString() = Hello World!
   typeof upperMessage = string
   upperMessage = HELLO WORLD!
   typeof subMessage = string
   subMessage = Hello

Converting to String objects on the fly:
   "...".length = 12
   "...".toUpperCase() = HELLO WORLD!