Javascript uses three logical operators: && (AND), || (OR), and ! (NOT). The first two take two boolean values and combine them, while the third takes a single boolean value and alters it. For example, if P and Q are the names of two boolean variables, then one could form P && Q (pronounced "P AND Q"), P || Q (pronounced "P OR Q"), and ! P (pronounced "NOT P").
The value of a boolean relation depends upon the values of the components. You can think of the expressions as asking a question. For example, P && Q asks, "Are P and Q (both) true?". P || Q asks, "Is (either) P or Q true?" Finally, ! P asks,"Is P not true?"
The tables below give the values for the each operator given possible values for P and Q. (These are called "truth tables".)
| P true | P false | |
|---|---|---|
| Q true | true | false |
| Q false | false | false |
| P true | P false | |
|---|---|---|
| Q true | true | true |
| Q false | true | false |
| P true | P false |
|---|---|
| false | true |