Is a variable defined?

• One must NEVER access an undefined variable

  • if in JavaScript that is linked to LiveConnect, one gets a Java error which requires restarting Netscape …..
  • If in less sensitive JavaScript, execution of script stops and action unpredictable

• Until page fully formed, any of its properties can be undefined

• Modern JavaScript allows one to test if variables are defined and so avoid these errors

• in a.b.c.d.e type reference, one must first test if a exists, then b, then ….

• WWutility.js includes

  • WW_isdefined(property) returns true if argument is defined as a property or method
  • WW_isitawindow(possibleframe) returns true if argument is a window or frame

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