Actionscript Cookbook

1.2. Checking Equality or Comparing Values

Problem

You want to check if two values are equal.

Solution

Use the equality (or inequality) or strict equality (or strict inequality) operator to compare two values. To check whether a value is a valid number, use isNaN( ).

Discussion

Equality expressions always return a Boolean value indicating whether the two values are equal. The equality (and inequality) operators come in both regular and strict flavors. The regular equality and inequality operators check whether the two expressions being compared can be resolved to the same value after converting them to the same datatype. For example, note that the string “6” and the number 6 are considered equal because the string “6” is converted to the number 6 before comparison:

trace(5 == 6);    // Displays: false
trace(6 == 6);    // Displays: true
trace(6 == "6");  // Displays: true
trace(5 == "6");  // Displays: false

The logical inequality operator (!=) returns false if two values are equal and true if they are not equal. If necessary, the operands are converted to the same datatype before the comparison:

trace(5 != 6);    // Displays: true
trace(6 != 6);    // Displays: false
trace(6 != "6");  // Displays: false
trace(5 != "6");  // Displays: true

On the other hand, the strict equality and inequality operators first check whether the values being compared are of the same datatype before performing the comparison. Differences in datatype cause the strict equality operator to return false and the strict inequality ...