Simple Javascript doesn't return anything

Question

I'm trying to learn some Javascript. I've written this code where it should return a, b, c, d and if the letter a is in the var letters, it should alert the message "Yes it is true".
When I run the code it doesn't return me anything.

Can anyone see why?

<script type="text/javascript">

    var letters = ["a", "b", "c", "d"]
    var numbers = ["one", "two", "three", "four"]

    for(x=0; x < letters.length; x++) {
        document.write(letters);
        if(a in letters)  {
            document.write("Yes it is true");
        }
    }

</script>

Scimonster · Accepted Answer · 2014-03-21 10:29:03Z

2

Instead of a in letters, you should use letters.indexOf('a') > -1. What's the difference?

To start with, a on its own is a variable. You have not defined this variable. Secondly, in does not search values, only keys. The keys of this array are 0,1,2,3. indexOf, on the other hand, does search values.

Additionally, you don't need a for loop for this.

edited Mar 21, 2014 at 10:29

answered Mar 21, 2014 at 10:23

Scimonster

33.4k10 gold badges79 silver badges92 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Raul Guiu · Accepted Answer · 2014-03-21 10:44:40Z

a is a variable that you have not defined, dont get confused with "a" (string)

And letters is the array. x is the index in the array that you are iterating through. letters[x] is an specific element with index x.

So, you could do "a" == letters[x] to compare to fix your code.

As a side note, I can suggest a better way of solving your problem.

You are trying to solve by iterating through the whole list and comparing the elements. That is ok, if you want to learn concepts like iteration, but thiscould be done a lot easier with inbuild methods in the string object, indexOf in this case.

<script type="text/javascript">

    var letters = ["a", "b", "c", "d"]
    var numbers = ["one", "two", "three", "four"]

    if(letters.indexOf("a") >= 0)  {
        document.write("Yes it is true");
    }

</script>

indexOf returns the index in the array of the element that you pass as argument, -1 if it is not in the array. So if this number is bigger or equal than zero means that the element exist in the array.

Karthick Kumar · Accepted Answer · 2014-03-21 10:19:57Z

0

please review this code, a is element of letters array

<script type="text/javascript">

    var letters = ["a", "b", "c", "d"]
    var numbers = ["one", "two", "three", "four"]

    for(x=0; x < letters.length; x++) {
        document.write(letters);
        if(letters[x]=='a')  {
            document.write("Yes it is true");
        }
    }

</script>

answered Mar 21, 2014 at 10:19

Karthick Kumar

2,3751 gold badge19 silver badges30 bronze badges

Comments

Gautam · Accepted Answer · 2014-03-21 10:21:11Z

0

you haven't define any varible with name a. you should use 'a' for checking in your aray

answered Mar 21, 2014 at 10:21

Gautam

3,3844 gold badges36 silver badges54 bronze badges

2 Comments

Julie24 Over a year ago

ah didn't see your comment :-) Thanks a lot

Scimonster Over a year ago

Using in is the wrong way to go anyways. in checks keys. See my answer.

Gerel tumen · Accepted Answer · 2014-03-21 10:43:10Z

0

You can access each element by its index



    if(letters[index]=='a')  {
        document.write("Yes it is true");
    }

answered Mar 21, 2014 at 10:43

Gerel tumen

1517 bronze badges

Comments

Siger · Accepted Answer · 2014-03-21 10:48:07Z

0

You can use letters.indexOf(a) instead of your for loop, it will returns the index of the variable 'a' inside the array 'letters' (-1 if not found). But before that you need to define the variable 'a'.

If you really want to keep the for loop, you should use it like this :

var a="a";
for(x=0; x < letters.length; x++) {
        document.write(letters);
        if(letters[x]==a)  {
            document.write("Yes it is true");
        }

answered Mar 21, 2014 at 10:48

Siger

92 bronze badges

Comments

Julie24 · Accepted Answer · 2014-03-21 10:22:05Z

-2

Answer:

for(x=0; x < letters.length; x++) {
        document.write(letters + "<br/>");
        if(a = letters)  {
            document.write("Yes it is true" + "<br/>");
        }
    }

Printout: a,b,c,d Yes it is true a,b,c,d Yes it is true a,b,c,d Yes it is true a,b,c,d Yes it is true

answered Mar 21, 2014 at 10:22

Julie24

2794 gold badges7 silver badges21 bronze badges

1 Comment

Scimonster Over a year ago

You're setting a variable, not comparing a string.

Collectives™ on Stack Overflow

Simple Javascript doesn't return anything

7 Answers 7

Comments

Comments

Comments

2 Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

2 Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related