CODEWITHSUNDEEP
javascriptarrays
user7435957
user7435957

Reputation:

Get All But The Last Element - JS

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?

Upvotes: 1

Views: 3977

Answers (3)

schroffl
schroffl

Reputation: 589

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.

Upvotes: 1

Gabriel K.
Gabriel K.

Reputation: 73

Try this condition for your if statement

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

Upvotes: 0

RomanPerekhrest
RomanPerekhrest

Reputation: 92904

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);

Upvotes: 2

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