Get All But The Last Element - JS

Question

I am working on a function that returns an array containing all but the last element of the array located at the given key.

-If the array is empty, it should return an empty array.
-If the property at the given key is not an array, it return an empty array.
-If there is no property at the key, it should return an empty array.

Here's my codes:

function getAllButLastElementOfProperty(obj, key) {
  var output = [];

   if ( key in obj && Array.isArray(obj[key]) && obj[key].length !== 0)
  {
        for(var i = 0; i < obj[key].length; i++ ){
          if(obj[key].length - 1){
              output.push(obj[key][i]);
          }

        }
       return output;
  }
}


var obj = {
  key: [1, 2, 3]
};
var output = getAllButLastElementOfProperty(obj, 'key');
console.log(output); // --> MUST RETURN [1,2]

My codes returns [1,2,3].

ANy idea what am I doing wrong?

I think you messed up the -1... try to use it in the for loop not in the if statement... :D — Janick Fischer
– Janick Fischer, Commented Jun 20, 2017 at 11:53
if(obj[key].length - 1){ always returns true (except for 0), so probably the mistake is there — Denny
– Denny, Commented Jun 20, 2017 at 11:54

RomanPerekhrest · Accepted Answer · 2017-06-20 11:53:52Z

2

The optimized getAllButLastElementOfProperty function version:

function getAllButLastElementOfProperty(obj, k) {
    if (!obj.hasOwnProperty(k) || !Array.isArray(obj[k]) || obj[k].length === 0) {
        return [];
    }
    return obj[k].slice(0, -1);  // getting all but the last element of the array
}

var obj = { key: [1, 2, 3] },
    output = getAllButLastElementOfProperty(obj, 'key');
    
console.log(output);

answered Jun 20, 2017 at 11:53

RomanPerekhrest

93.1k4 gold badges75 silver badges112 bronze badges

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

Comments

schroffl · Accepted Answer · 2017-06-20 12:26:21Z

You could generalize your function by making it take an array as an argument and then calling getAllButLastElement(obj.key). This also returns an empty array if the object does not have the property key.

This could then be implemented like this:

function getAllButLastElement(arr) {
  if(!Array.isArray(arr))
    return []; // Return an empty array

  return arr.slice(0, -1);
}

let obj = {
  'key': [ 1, 2, 3 ],
  'empty': [ ]
};

console.log('obj.key:', getAllButLastElement(obj.key)); // Proper Array
console.log('obj.empty:', getAllButLastElement(obj.empty)); // Empty Array
console.log('obj.unknown:', getAllButLastElement(obj.unkown)); // Property does not exist

Passing a negative number to Array.prototype.slice accesses the array from the end. In the snippet this means that we take everything from the first element up to the index arr.length - 1. If we were to use arr.slice(-1) this would only return the last element (still as an array of course) which is the exact opposite of what you want.

Gabriel K. · Accepted Answer · 2017-06-20 11:57:49Z

0

Try this condition for your if statement

if(i !== obj[key].length - 1){
          output.push(obj[key][i]);
      }

answered Jun 20, 2017 at 11:57

Gabriel K.

731 gold badge3 silver badges11 bronze badges

Collectives™ on Stack Overflow

Get All But The Last Element - JS

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related