CODEWITHSUNDEEP
javascriptbooleantruthiness
Alexander Coffman
Alexander Coffman

Reputation: 543

Is there a way to clarify the true and false statements in this JS?

I've been working on learning JS, and I can't seem to figure out why my boolean values keep coming back either always true or always false.

So I believe I understand the basics of the truthy/falsy situation in JS, but I can't seem to get it right. I know that there are data type issues, (can't make different data types do different things).

function lastCharacter(char1, char2) {
  if (char1[-1] === '' && char2[-1] === '') {
    return true;
  } else {
    return false;
  }
}

console.log(lastCharacter('apple', 'pumpkine'));

Or

function lastCharacter(char1, char2) {
  if (char1[-1] === char2[-1]) {
    return true;
  } else {
    return false;
  }
}

console.log(lastCharacter('apple', 'pumpkina'));

Define a function lastCharacter that accepts two strings as arguments. lastCharacter should return true if both strings end with the same character. Otherwise, lastCharacter should return false.

They either return always true or always false. Can anyone help me?

Upvotes: 1

Views: 320

Answers (4)

Nina Scholz
Nina Scholz

Reputation: 386604

You need a different method for getting the last character of a string, preferably with String#slice and a negative value for getting the last one. Then compare and return the result.

function lastCharacter(string1, string2) {
    return string1.slice(-1) === string2.slice(-1);
}

console.log(lastCharacter('apple', 'pumpkine'));

A comparison between taking the last character of an empty string by using an index -1 which returns undefined and slice, which returns an empty string.

var x = '';

console.log('#' + x.slice(-1) + '#');
console.log('#' + x[x.length -1] + '#');

Upvotes: 3

Jonas Wilms
Jonas Wilms

Reputation: 138267

There are no negative array indexes in JavaScript, instead of char1[-1] you have to use char1[char1.length - 1].

Accessing one of a strings characters (e.g. "abc[1]) will always have a length of 1, it will never be equal to "". Your second function makes more sense.

Also

 if(condition) { return true; } else { return false; }

is equal to

 return condition;

Upvotes: 0

Pointy
Pointy

Reputation: 413727

The notation [-1] does not implicitly mean "one character from the end of the string" in JavaScript. You can use str[str.length - 1]. (If you expect possible empty source strings, you'd want to check for that too to avoid ending up with exactly the same problem.)

Instead of an if/else that returns either true or false, just return the results of the logical expression:

    return char1[char1.length - 1] === '' && char2[char2.length - 1] === '';

Both the === comparisons return either true or false anyway, so the overall expression value has to be one of those. In general however if you want to make absolutely sure that you end up with a boolean, you can prefix an expression with !! to force the standard JavaScript "truthy-falsy" evaluation:

    return !!(expression);

Upvotes: 0

Code Maniac
Code Maniac

Reputation: 37755

You can use slice 

function lastCharacter(char1, char2) {
  return char1.slice(-1) === char2.slice(-1)
}

console.log(lastCharacter('apple', 'pumpkina'));
console.log(lastCharacter('apple', 'snake'));

Or you can just access the last index

function lastCharacter(char1, char2) {
  return char1[char1.length-1] === char2[char2.length-1]
}

console.log(lastCharacter('apple', 'pumpkina'));
console.log(lastCharacter('apple', 'snake'));

Upvotes: 2

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