Return boolean value through multiple functions

Question

I have some Javascript code that needs to end with either a true or false value being returned. However, when the true/false value is computed, the original value has passed through multiple functions, like so:

var txt = 'foo'    
function one(txt) {
if(txt == 'foo') { two(txt); }
}
function two(txt) {
if(txt == 'foo') { three(txt); }
}
function three(txt) {
if(txt == 'foo') { return true; }
else { return false; }
}

Obviously this example has little point but it gets the general point across. What I need to do to it is return the true (or false) value from function three() all the way back to function one(), and then have function one() return that value to whatever called it. I am assuming I have to go back through function two() to get back to one, is there a way I can do this with a variable? Just an idea. Thanks very much for any help!

Maybe I don't get the question but just write return two(txt); and return three(txt); won't work? — Fabio Filippi
– Fabio Filippi, Commented Jul 12, 2010 at 17:04

Daniel Vassallo · Accepted Answer · 2010-07-12 17:11:40Z

5

You may want to try the following (if I understood your question correctly):

function one(txt) {
   if(txt == 'foo') return two(txt);
   else return false;
}

function two(txt) {
   if(txt == 'foo') return three(txt);
   else return false;
}

function three(txt) {
   if(txt == 'foo') return true;
   else return false;
}

edited Jul 12, 2010 at 17:11

answered Jul 12, 2010 at 17:04

Daniel Vassallo

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2 Comments

Gabe Moothart Over a year ago

You can coerce to boolean - return two( new Boolean(txt) ); or return two( !!txt ); - without needing the || false.

Daniel Vassallo Over a year ago

@Fabio: I removed the || false part. It isn't needed if all functions return either true or false.

dhorn · Accepted Answer · 2010-07-12 17:03:31Z

2

Change the calls to three() and two() to return three() and return two().

answered Jul 12, 2010 at 17:03

dhorn

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1 Comment

Daniel Vassallo Over a year ago

That would still return undefined if you pass something other than foo to the one() function.

tzaman · Accepted Answer · 2010-07-12 17:14:00Z

0

If you like ternary operators:

function one(txt) {
    return (txt == 'foo') ? two(txt) : false;
}
function two(txt) {
    return (txt == 'foo') ? three(txt) : false;
}
function three(txt) {
    return (txt == 'foo');
}

answered Jul 12, 2010 at 17:14

tzaman

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Comments

Matt Evanoff · Accepted Answer · 2010-07-12 17:15:11Z

0

You can do it like people said above, or you can declare a variable outside the functions so it is global and just refer to it. It is not considered great practice, but it will work.

answered Jul 12, 2010 at 17:15

Matt Evanoff

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Comments

Josh K · Accepted Answer · 2010-07-12 19:19:01Z

0

Try:

var txt = 'foo'    
function one(txt) {
if(txt == 'foo') return two(txt); 
 else return false;
}
function two(txt) {
if(txt == 'foo')  return three(txt); 
 else return false;
}
function three(txt) {
if(txt == 'foo')  return true; 
else return false; 
}

edited Jul 12, 2010 at 19:19

answered Jul 12, 2010 at 17:05

Josh K

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1 Comment

tzaman Over a year ago

one and two also need else cases, or they won't return anything when the condition is false.

BarryBurns · Accepted Answer · 2013-02-19 20:03:51Z

0

var txt = 'foo';

function one(txt) {
   return two(txt); 
}

function two(txt) {
    return three(txt); 
}

function three(txt) {
    return txt == 'foo'
}

answered Feb 19, 2013 at 20:03

BarryBurns

11

3 Comments

junix Over a year ago

A few more words about why you suggest this code would be nice.

BarryBurns Over a year ago

I think it's best because it treats the boolean like any other type. It is also the simplest, needing no if's or else's. The boolean is created with the test in function 3, and passed up the stack.

Jack Viers Over a year ago

@BarryBurns is correct. This is an example of function composition. one txt === (two of three) txt. This is preferable to the boolean early exit examples because you can avoid using a conditional to return a boolean (this is redundant since a boolean condition evaluates to true or false, and it becomes easy to return a contradiction, which is confusing), and also allows the the creation of complex conditionals by composing more functions together.

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