I am new to JavaScript and I know I did something wrong because I keep getting true as a result. Can someone please point out my mistake? Thanks in advance.

function checkForVowel(x){
   if(x == "a", "e", "i", "o", "u"){
       document.write("true");
   }else{
       document.write("false");
   }
}

checkForVowel("n");

I am new to JavaScript and I know I did something wrong because I keep getting true as a result. Can someone please point out my mistake? Thanks in advance.

function checkForVowel(x){
   if(x == "a", "e", "i", "o", "u"){
       document.write("true");
   }else{
       document.write("false");
   }
}

checkForVowel("n");

• javascript
• if-statement

• 1 Take a look here stackoverflow./questions/5488028/… there are many ways to check for a vowels – G-Man Commented Jun 7, 2012 at 1:27

3 Answers 3

JavaScript's parison operator isn't magic; you'll need to do each parison separately. You can check for "any of these" using a logical OR, ||:

if(x == "a" || x == "e" || x == "i" || x == "o" || x == "u")

Or, since you have many single-character strings, you can make use of indexOf. But the above might be easier to understand if you're just starting out.

if(x.length === 1 && 'aeiou'.indexOf(x) > -1)

As for the reason you keep getting true, it's that , is actually an operator in JavaScript, mainly invented to confuse people¹. It evaluates its left side, then evaluates its right side, and returns the right side. So your expression boils down like this:

if(x == "a", "e", "i", "o", "u")
if("e", "i", "o", "u")
if("i", "o", "u")
if("o", "u")
if("u")

Which is a truthy value.

_{¹ Not actually.}

Sometimes the code is a lot cleaner to test against a data structure than use lots of if/else code. Which is faster may depend upon the specific browser engine and how many parisons you have. This one looks to see if the string is present in a string of vowels:

var vowels = "aeiou";

function checkForVowel(x) {
    return(vowels.indexOf(x.toLowerCase()) >= 0);
}

This one tests to see if the test char is in a javascript object which isn't needed here, but is another interesting way to test if something is in a set:

var vowels = {a: true, e: true, i: true, o: true, u: true};

function checkForVowel(x) {
    return(x.toLowerCase() in vowels);
}

I don't know why, but no one suggested this. :/

function checkForVowel(x){
    document.write(/[aeiou]/i.test(x));   //Clearly this is even simpler than
}                                         // other methods.

Or

function checkForVowel(x){
   if(x.search(/[aeiou]/i) != -1){
       document.write("true");
   }else{
       document.write("false");
   }
}