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DIFFICULTY LEVEL: BEGINNER
Assumes good beginner level knowledge and/or familiarity of Scripting in ServiceNow.
JavaScript Switch Statements - A useful alternative to infinite if then/else if/else statements!
I see this a lot in code scripts: A run-on if (...) {} else if (...) {} else if (...) {} else if (...) {} else if (...) {} else {} statement. While they have their uses (especially with mixed variable checks); they can be confusing to a maintenance coder (even if well commented). Might I suggest that if you find yourself faced with the need for a large if/then statement that examines the same variable that you use a 'switch' statement instead. With this sort of situation; 'switch' statements can organize the code in a more maintainable manner, and allow for easier condition additions at a later time.
NOTE: I ran all of these examples Scripts - Background.
Here is an example. First the if then/else if, and then the same thing re-written as a 'switch' statement:
// If/then/else if/else
var myCheck = 'yellow';
var temperature = '0 F';
if (myCheck == 'green') {
gs.info("(if) All is well with the 'verse!");
temperature = '72 F';
}
else if (myCheck == 'yellow' || myCheck == 'yellow-orange') {
gs.info('(if) The Dallas Cowboys really reside in Arlington.');
temperature = '85 F';
}
else if (myCheck == 'orange' || myCheck == 'orange-red') {
if (myCheck == 'orange') {
gs.info('(if) Temperatures in Dallas are hotter than in Houston, and the humidity is worse!!!');
temperature = '95 F';
}
if (myCheck == 'orange' || myCheck == 'orange-red') {
gs.info('(if) Wait, it is hotter than I thought!!');
temperature = '98 F';
}
}
else if (myCheck == 'red') {
gs.info('(if) Red alert! Red alert! Danger, danger Will Robinson!');
temperature = '100 F';
}
else {
gs.info('(if) I have no idea what the myCheck value means!');
temperature = '>100 F!';
}
gs.info('(if) The temperature is: ' + temperature);
Will give the following result (it is our baseline):
So here is the basic switch alternative:
// switch analog - basic
var myCheck = 'yellow';
var temperature = '0 F';
switch (myCheck) {
case 'green':
gs.info("(switch-basic) All is well with the 'verse!");
temperature = '72 F';
break;
case 'yellow':
// No break here. Falls through.
case 'yellow-orange':
gs.info('(switch-basic) The Dallas Cowboys really reside in Arlington.');
temperature = '85 F';
break;
case 'orange':
gs.info('(switch-basic) Temperatures in Dallas are hotter than in Houston, and the humidity is worse!!!');
temperature = '95 F';
break;
case 'orange-red':
gs.info('(switch-basic) Wait, it is hotter than I thought!!');
temperature = '98 F';
break;
case 'red':
gs.info('(switch-basic) Red alert! Red alert! Danger, danger Will Robinson!');
temperature = '100 F';
break;
default:
gs.info('(switch-basic) I have no idea what the myCheck value means!');
temperature = '>100 F';
break;
}
gs.info('(switch-basic) The temperature is: ' + temperature);
Will give the following result:
Aaaand, it is the same; except the label of course.
Notice that with the 'switch' it is a simple matter to add new conditions ('else if') by inserting a new 'case' statement. If you want to add an 'OR' into the mix simply add a new 'case' condition before the code you want executed (yellow OR yellow-orange). The 'default' statement acts as the catch-all (the same as the 'else' statement in the 'if/then' structure). BTW, the 'default' statement is optional (the same as the 'else' is optional in the 'if then/else if/else' statement). Don't forget the 'break' statement as this serves to keep the program from executing the lines immediately following! Try out the 'orange' value to see what I mean.
Another approach on the switch statement gives the developer much more flexibility on the Case statements. For example:
// switch statement - flexible version
var myCheck = 'yellow';
var temperature = '0 F';
switch (true) {
case (myCheck == 'green'):
gs.info("(switch-flexible) All is well with the 'verse!");
temperature = '72 F';
break;
case (myCheck == 'yellow' || myCheck=='yellow-orange'):
gs.info('(switch-flexible) The Dallas Cowboys really reside in Arlington.');
temperature = '85 F';
break;
case (myCheck == 'orange'):
gs.info('(switch-flexible) Temperatures in Dallas are hotter than in Houston, and the humidity is worse!!!');
temperature = '95 F';
break;
case (myCheck == 'orange-red'):
gs.info('(switch-flexible) Wait, it is hotter than I thought!!');
temperature = '98 F';
break;
case (myCheck == 'red'):
gs.info('(switch-flexible) Red alert! Red alert! Danger, danger Will Robinson!');
temperature = '100 F';
break;
default:
gs.info('(switch-flexible) I have no idea what the myCheck value means!');
temperature = '>100 F';
break;
}
gs.info('(switch-flexible) The temperature is: ' + temperature);
Will give the following, same, result:
There you go, another tool for your toolbox!
Enjoy!
Steven Bell.
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Originally published on: 07-19-2015 08:16 AM
I updated the code and brought the article into alignment with my new formatting standard.
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