Explain JavaScript logical not operator _javascript tips

In JavaScript, the logical NOT operator is the same as the logical not operator in C and Java, and is represented by an exclamation point (!). Unlike a logical OR and a logical AND operator, the logical NOT operator returns a Boolean value.

the logical NOT operator behaves as follows:

• Returns False if the OP count is an object
• If the OP count is number 0, return True
• If the OP count is any number other than 0, return false
• Returns True if the OP count is null
• Returns True if the OP count is NaN
• If the OP count is undefined, there's a mistake.

The test script is as follows:

<script type= "Text/javascript" > var bfalse = false;//op arithmetic is the number of bool type var sred = "Red";/op arithmetic is string var Izero = 0;// Op count is 0 var ithreefourfive = 345;//arithmetic is 0 other than any number var oobject = new Object ();//object var onull=null;//arithmetic is null var ound efined;//is the undifined var onan=parseint ("abc");//Use the Parseint method to convert the attempt string abc to an integer, because ABC is not a number and therefore cannot be turned, so the result of the return is Nan/* WRI The Teln () method is almost the same as the write () method, except that the former will add a newline character after any supplied string.
  In HTML, this usually only produces a space later, but if the <PRE> and <XMP> identities are used, the line break is interpreted and displayed in the browser.
 * * Document.writeln ("<XMP>");
 Document.writeln ("Onan=parseint" (\ abc\) Returns the result is "+onan");
 Document.writeln (The result of the number of types BOOL and! Operator operations is: "+ (!bfalse));
 The result of Document.writeln ("String sred and! Operator operations is:" + (!sred)); Document.writeln (The result of the number 0 and! Operator operation is: "+ (!izero));//If the arithmetic is number 0, return True Document.writeln (the result of the number 345 and! Operator operation is:" + (!) ithreefourfive);//If the OP count is any number other than 0, return false Document.writeln ("The result of the object Oobject and! Operator operation is:" + (!oobject)); If the OP count is an object, return False Document.writeln (the result of the Nan and! Operator operation is: "+ (!onaN); Returns True Document.writeln (the result after null and! Operator operation is: "+ (!onull));//If the shipping count is null, return True Document.writeln (" und
 Ifined and! The result of the operator operation is: "+ (!oundefined)); 
 The result of Document.writeln ("Undefined string sbule and! Operator operations is:" + (!sbule));//sbule there is no definition before, that is, Sbule is the undefined, so there is an error here.
 Document.writeln ("</XMP>"); </script>

Run Result:

　　

You can also use the logical not operator when judging a Boolean value for a JavaScript variable. Doing so requires the use of two not operators in one line of code. Regardless of the type of OP count, the first not operator returns a Boolean value, and the second not negates the Boolean value, giving the variable a true boolean value. It is a useful technique to use the NOT operator to determine the Boolean value of a JavaScript variable, as long as you know the Boolean value of the variable, then use the variable for && or | | Operation, you can quickly know the result of the operation.
The test script is as follows:

<script type= "Text/javascript" > var bfalse = false;//op arithmetic is the number of bool type var sred = "Red";/op arithmetic is string var Izero = 0;// Op count is 0 var ithreefourfive = 345;//arithmetic is 0 other than any number var oobject = new Object ();//object var onull=null;//arithmetic is null var ound
 efined;//is the undifined var onan=parseint ("abc");//Use the Parseint method to convert the attempt string abc to an integer, because ABC is not a number and therefore cannot be turned, so the result of the return is Nan/* You can also use the logical not operator when judging a Boolean value for a JavaScript variable.
 Doing so requires the use of two not operators in one line of code. The first not operator returns a Boolean value, regardless of the type of OP count.
 The second not negates the Boolean value, giving the true Boolean value of the variable.
 * * document.write ("<PRE>"); Document.writeln (The logical value of the Boolean false is "+" (!!).
 Bfalse)); Document.writeln ("The logical value of the string sred is" + (!!)
 sred)); Document.writeln ("The logical value of the number 0 is" + (!!)
 Izero)); Document.writeln ("The logical value of the number 345 is" + (!!)
 ithreefourfive)); Document.writeln ("The logical value of Object objects is" + (!!)
 Oobject)); Document.writeln ("Nan's logical value is:" + (!!)
 ONaN)); Document.writeln ("Null logical value is" + (!!)
 Onull)); Document.writeln ("Undefined logical value is" + (!!)
 oundefined));
 document.write ("</PRE>"); </script>

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