Why this JavaScript code doesn't work?

Question

I have for loop which goes through the array with arguments. When next argument is "?", "&" or "||", it shouldn't add comma, however, it always adds. I couldn't understand why, here is the code:

var args = ["arg1","arg2","?","arg3"];
var query = "";
for (var i = 0; i < args.length; i++) {
		switch (args[i]) {
			case "?":
				query += " where ";
				break;
			case "&":
				query += " and ";
				break;
			case "||":
				query += " or ";
				break;
			default:
				if (args[i+1] != "?"); 
				{
					query += args[i] + ", ";
					break;
				}
				query += args[i] + " ";
				break;
		}
	}
document.write(query);

When I type this (this is splitted by " " and sent to array args):

arg1 arg2 ? arg3

It prints it like this:

arg1, arg2, where arg3, // while it should be arg1, arg2 where arg3,

Thanks for helping people, problem was caused by an extern script. And yes, I removed semicolon ;)

• Nina Scholz: where is it different arg1, arg2, where arg3, // while it should be arg1, arg2 where arg3,?
• Pointy: @NinaScholz that comma after arg2 before where is not wanted apparently.
• Teemu: Prints where? You're probably "printing" an array, and its toString method adds the comma.
• Nikola Stojaković: @Teemu When I print query variable. Query variable is string and is defined before this loop.
• 1983: if (args[i+1] != "?"); oops!

Answer 1

Your if statement is broken:

 if (args[i+1] != "?"); // <---- remove that semicolon
 {
 query += args[i] + ", ";
 break;
 }

You've got a stray semicolon. It is not a syntax error, but it means the if doesn't do anything. The code that adds the comma always runs, and exits the switch before the code that doesn't add the comma.

• Pointy: @CayceK I have, and I've also run the code. It works without the semicolon.
• Nikola Stojaković: Thanks for trying to help out but I solved this. This problem was caused by another array from extern script, now everything works. Thanks for answers anyway.
• Pointy: @Nikola trust me, you want to get rid of that semicolon.
• Syed Ekram Uddin: @Nikola The problem is ppl vote for the wrong answer without knowing the whole story (for comments here and there). This could misguide other persons to find out the right answer, which is lies in a comment.
• Pointy: @SyedEkramUddinEmon Except in this case it's not the wrong answer. That semicolon dramatically changes the meaning of the code.

Answer 2

You have a semicolon between your if and your block:

if (args[i+1] != "?"); 

Should be

if (args[i+1] != "?")

Answer 3

There may be completely different ways to solve this problem which would make your code easier to extend without deepening trees of if or switch

A quick example,

// define some dictionaries
let logicDict = Object.assign(Object.create(null), {
 '?': 'where',
 '&': 'and',
 '||': 'or'
});
// define some flags
let noComma = false;
// reduce your array
['arg1', 'arg2', '?', 'arg3'].reduceRight((str, e) => {
 if (e in logicDict) {
 noComma = true;
 return logicDict[e] + ' ' + str;
 }
 if (!noComma) e += ',';
 noComma = false;
 return e + ' ' + str;
}, '').slice(0, -1);
// "arg1, arg2 where arg3,"

• Nikola Stojaković: This is very interesting. Thanks!

Answer 4

Thanks for noticing semicolon guys, problem was caused by an extern script.

• Pointy: Your script, modified only to declare query and to hook args up to process.argv as a Node.js program, did not work with the semicolon but it did work correctly once the semicolon was removed.
• 1983: Indeed. Leave that semicolon in and it'll still be wrong.
• Nikola Stojaković: LOL, I said thanks for noticing semicolon guys, and you're still complaining about ..king semicolon?! Yes, that was an error, I know! No matter how it sounds stupid, but it actually worked even with that semicolon (and I'm really not sure how, but I removed it). I won't repeat this guys. Please, there's nothing new to say about this. Thanks for noticing, again!