AS3: NaN as Nullable Numbers September 23, 2007
One major change from AS2 was the removal of Numbers being nullable, this was useful for determining if something had been given a value or not, and setting it to a default. One workaround is using NaN, which can be used on the function initializer:
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function testNum(num:Number = NaN) {
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if (isNaN(num)) {
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trace(num + " no num");
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} else {
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trace("has num: " + num);
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}
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}
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/////////// BEGIN TEST /////////////
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var numA:Number; //NaN
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testNum(); // NaN no num
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testNum(numA); //NaN no num
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numA = -1;
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testNum(numA); //has num: -1
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numA = 0;
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testNum(numA); //has num: 0
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numA = 1;
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testNum(numA); //has num: 1
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