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Chapter 8
Operators

This section provides information about changes to the equality operators and the new delete operator.

If the <SCRIPT> tag uses LANGUAGE=JavaScript1.2, the equality operators (== and !=) work differently. This section describes how the equality operators work without LANGUAGE=JavaScript1.2 and how they work with LANGUAGE=JavaScript1.2. For instructions on writing code to convert strings and numbers, see "Data Conversion".

The following describes how the equality operators (== and !=) worked in previous versions of JavaScript and how they work in JavaScript 1.2 when LANGUAGE=JavaScript1.2 is not used in the <SCRIPT> tag. Note that if LANGUAGE=JavaScript, and LANGUAGE=JavaScript1.1 are used, the equality operators maintain their previous behavior.

• If both operands are objects, compare object references.
• If either operand is null, convert the other operand to an object and compare references.
• If one operand is a string and the other is an object, convert the object to a string and compare string characters.
• Otherwise, convert both operands to numbers and compare numeric identity.

If LANGUAGE=JavaScript1.2 is used in the <SCRIPT> tag, the equality operators (== and != ) behave as follows:

• They never attempt to convert operands from one type to another. To convert operands, do the following:
• They always compare identity of like-typed operands. If the operands do not have like type, they are not equal.

To write JavaScript code that converts strings to numbers and numbers to strings in the different versions of Navigator, follow these guidelines:

When writing for all versions of Navigator:

• To convert x to a string, use " " + x. For example,

  "" + 3 == "3"

• To convert x to a number, use (x - 0). For example,

  "3" - 0 == 3

• To convert x to a Boolean, use !!x. For example,

  !!null == false

When writing for Navigator 4.0 only:

• To convert x to a string, in addition to " " + x, you can use String(x). For example,

  var x = 3
  String(x) = "3"

• To convert x to a number, in addition to (x - 0), you can use Number(x). For example,

  var x = "3"
  Number(x) = 3

• To convert x to a Boolean, in addition to !!x, you can use Boolean(x). For example,

  var x = null
  Boolean(x) = false

<SCRIPT>
document.write("3" == 3);
</SCRIPT>

<SCRIPT>
document.write(("3"-0) == 3);
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript">
document.write("3" == 3);
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.1">
document.write("3" == 3);
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.2">
document.write("3" == 3);
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.2">
document.write(("3"-0) == 3);
</SCRIPT>

<SCRIPT LANGUAGE="JavaScript1.2">
document.write(String(3) == "3");
</SCRIPT>

delete objectName.property
delete objectname[index]
delete property

index is an integer representing the location of an element in an array.

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Last Updated: 10/22/97 11:48:09