May 3, 2000 - Detecting Object-Property Relationship
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May 3, 2000 Detecting Object-Property Relationship  Tips: May 2000
Yehuda Shiran, Ph.D.
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in operator checks if a given property is defined for a given object. Suppose the object line is of type Array:
line = new Array("aaa", "bbb", "ccc", "ddd", "eee");
We know that the object line inherited the Array's properties such as its length. If we check whether length is in line (length in line), we should get a true value. Notice that the array should not be empty, or else the returned answer will be a false value.
Similarly, the method hasOwnProperty does exactly what the in operator does. The expression:
line.hasOwnProperty(length)should return a true value.
The method propertyIsEnumerable() checks, again, that a given property belongs to a given object. Once it belongs, it is automatically enumerable in for...in loops. The for...in loop loops through the existing properties of a given object. The check line.propertyIsEnumerable(length) should return a true value.
