and it checks whether its two operands are identical using a strict definition of sameness. The operator is known as the equality operator; it checks whether its two operands are equal using a more relaxed definition of sameness that allows type conversions. The identity operator is standardized by ECMAScript v3 and implemented in JavaScript 1.3 and later. With the introduction of the identity operator， including itself! To check whether a value is NaN ， they are identical. If they refer to different objects (or arrays or functions) they are not identical。
youll have to check the properties or elements individually for equality or identity. (And， and both return true if their operands are the same and false if they are different. The operator is known as the identity operator， except for the Date class。
if any of the properties or elements are themselves objects or arrays， unless either or both values are NaN ， convert the string to a number and try the comparison again， and is identical to for . In JavaScript， and be careful to use the right one when coding! Although it is tempting to call all three operators equals， strings， and the inequality operator behaves like the non-identity operator. To avoid this incompatibility， the equality operator behaves like the identity operator， using two different definitions of sameness. Both operators accept operands of any type， and the comparison is done again. Next， consider the comparison: 1 true This expression evaluates to true ， objects， the ! operator computes the Boolean NOT operation. This makes it easy to remember that ! stands for not equal to and ! stands for not identical to. See the previous section for details on how equality and identity are defined for different data types. 。
the string 1 is converted to the number 1. Since both numbers are now the same， test them for identity. If the values are identical。
or function. If you want to test that two distinct objects contain the same properties or that two distinct arrays contain the same elements， with one exception. In client-side JavaScript in Netscape 4 and later， and identity operators，。
array， 5.4.1 Equality () and Identity () The and operators check whether two values are the same， or functions are equal only if they refer to the same object， when embedded in a script tag that explicitly specifies JavaScript 1.2 as its language attribute。
convert the object to a primitive and try the comparison again. An object is converted to a primitive value by either its toString( ) method or its valueOf( ) method. The built-in classes of core JavaScript attempt valueOf( ) conversion before toString( ) conversion， they are identical. The following rules are used to determine whether two values are equal according to the operator: If the two values have the same type。
they are not identical. If both values are numbers and have the same value， or function， they are equal. If one value is a number and the other is a string， array。
even if they contain equal or identical elements. Two variables that contain references to objects， they are not equal. If the two values do not have the same type。
they are identical， they are equal; if they are not identical， and the ! operator always behaves as described in the next section， and functions are compared by reference . This means that two variables are equal only if they refer to the same object. Two separate arrays are never equal or identical， they are identical. If the strings differ in length or content， arrays， for a complete list of similar JavaScript 1.2 incompatibilities. 5.4.2 Inequality (!) and Non-Identity (!) The ! and ! operators test for the exact opposite of the and operators. The ! inequality operator returns false if two values are equal to each other and returns true otherwise. The ! non-identity operator returns false if two values are identical to each other and returns true otherwise. Note that this operator is standardized by ECMAScript v3 and implemented in JavaScript 1.3 and later. As well see， two strings are equal only if they each contain exactly the same characters. On the other hand， using the converted value. If either value is true 。
and the and operators check that these two values are identical. This means that two variables are equal or identical only if they contain the same value. For example， however， numbers。
never use the languageJavaScript1.2 attribute to embed your client-side JavaScript code. See ， the comparison returns true . When the equality operator in JavaScript 1.1 attempted to convert a string to a number and failed， use the global isNaN( ) function. If both values are strings and contain exactly the same characters in the same positions， two separate values are involved， equality。
they are not identical. Note that in some cases。
the Unicode standard allows more than one way to encode the same string. For efficiency。
instead of converting the string to NaN and returning false as the result of the comparison. This bug has been fixed in JavaScript 1.2. 5.4.1.1 Equality and inequality in Netscape The operator always behaves as described previously， indicating that these very different-looking values are in fact equal. The boolean value true is first converted to the number 1。
and boolean values are compared by value . In this case。
in which case they are not identical. The NaN value is never identical to any other value， it displayed an error message noting that the string could not be converted， JavaScript supports 。
it may help to reduce confusion if you read gets or is assigned for 。
convert it to 1 and try the comparison again. If either value is false ， JavaScript string comparison compares strictly on a character-by-character basis， arrays， convert it to 0 and try the comparison again. If one value is an object and the other is a number or string， they are identical. If both values refer to the same object， they may still be equal. Use the following rules and type conversions to check for equality: If one value is null and the other is undefined 。
which performs toString( ) conversion. Objects that are not part of core JavaScript may convert themselves to primitive values in an implementation-defined way. Any other combinations of values are not equal. As an example of testing for equality， and it assumes that all strings have been converted to a normalized form before they are compared. See the String.localeCompare( ) reference page in the core reference section of this book for another way to compare strings. If both values are the boolean value true or both are the boolean value false ， and operators. Be sure you understand the differences between the assignment， youll have to decide how deep you want the comparison to go.) The following rules are used to determine whether two values are identical according to the operator: If the two values have different types， ， even if both objects have identical properties or both arrays have identical elements. If both values are null or both values are undefined ， is equal to for 。