JavaScript logic operation

Compare operation returns a single result, true or false. A plurality of logical operation may be operating together for comparison compare.

Operators

Series operator	name	Explanation
&&	Logic and	A plurality of inspection conditions, if the conditions checked are true returns true
\|\|	Logical or	A plurality of inspection conditions if any of the conditions to be checked are true returns true
!	Logical NOT	Boolean value inversion

Logic and

1 true && true //返回true

2 to true && false // returns false

3 false to true && // returns false

4 false && false // returns false

Logical or

1 returns true true || true //

2 returns true true || false //

3 returns true false || true //

4 false || false // returns false

Logical NOT

 
        ! 
        true  
        // 
        返回 
        false 
       
        ! 
        false  
        // 
        返回 
        true

Short-circuit conditions

Logical expression left to right. If the first condition to provide sufficient information for the final result, there is no requirement that the latter calculation.

 
        false 
        && 任何条件

Here is false, it is not necessary at this time to go back calculation expression, because the entire result can not be true.

 
        true 
        && 任何条件

Here is true, it is not necessary at this time to go back calculation expression, as it has at least one result is true.

Example:

 1 <!DOCTYPE HTML>
 2 <html lang="zh">
 3 <body>
 4 <script>
 5     document.write(3>2 && 3<2);//逻辑与(必须都为true，否则为false)
 6     document.write('<br>');
 7    document.write(7>3 && 7>4);
 8    document.write('<br>');
 . 9     document.write ( . 3 * . 4 == . 4 * . 3  ||  2 * . 5 == . 4 * . 5 ); // logical OR (wherein a is true, compared to true) 
10      document.write ( ' <br> ' );
 . 11     document.write ( . 7 < . 3  ||  . 7 < . 4 );
 12 is     document.write ( ' <br> ' );
 13 is     document.write ( ! . 7 > . 3 ); //The logical negation value of the Boolean negation 
14  </ Script > 
15  </ body > 
16  </ HTML >