I am making a function that returns greatest mmon prefix. When input is: ["flower","flow","flight"], output should be: "fl". But there is an exception, when input is an empty array the output should be an empty string. This is where my function is not working.

var longestCommonPrefix = function(strs) {
    let prefix = '';
    let word = '';

    for (let i = 0; i < strs.length; i++){
        for(let j = i + 1; j < strs.length; j++) {
          for (let k = 0; strs[i][k] === strs[j][k]; k++) {
              prefix += strs[i][k];
              //console.log(prefix);
          }
          prefix += ',';
          //console.log(prefix);
        }
    }
    prefix = prefix.split(',').sort().slice(1);
    console.log(prefix);
    // if(prefix[0].length === 0) {
    //     return "";
    // }
    return prefix[0];
};
console.log(longestCommonPrefix(["flower","flow","flight"]));

I am making a function that returns greatest mmon prefix. When input is: ["flower","flow","flight"], output should be: "fl". But there is an exception, when input is an empty array the output should be an empty string. This is where my function is not working.

var longestCommonPrefix = function(strs) {
    let prefix = '';
    let word = '';

    for (let i = 0; i < strs.length; i++){
        for(let j = i + 1; j < strs.length; j++) {
          for (let k = 0; strs[i][k] === strs[j][k]; k++) {
              prefix += strs[i][k];
              //console.log(prefix);
          }
          prefix += ',';
          //console.log(prefix);
        }
    }
    prefix = prefix.split(',').sort().slice(1);
    console.log(prefix);
    // if(prefix[0].length === 0) {
    //     return "";
    // }
    return prefix[0];
};
console.log(longestCommonPrefix(["flower","flow","flight"]));

• javascript

Share Improve this question Follow edited Jun 5, 2023 at 12:38 Reporter 3,93655 gold badges3535 silver badges4949 bronze badges asked May 7, 2020 at 17:13 user10321333user10321333 3

• 5 show full code please – brk Commented May 7, 2020 at 17:14
• 1 my guess is that you have a callback function and you return a value inside of it, but its just a guess. show us your code – Ilijanovic Commented May 7, 2020 at 17:18
• Posted the code @brk – user10321333 Commented May 7, 2020 at 21:13

Add a ment  | 

6 Answers 6

Sorted by: Reset to default 3

Following should work:

function returnEmptyIfNull(arr) {
    if(!arr?.length)
        return "";
    return "not empty";
}

Check the array for null and a size of 0. If either of these conditions are true, return an empty string.

function joinItems(items) {
  return items == null || items.length === 0 ? '' : items.join(', ');
}

console.log(joinItems(['Hello', 'World'])); // "Hello, World"
console.log(joinItems([]));                 // ""

You can simplify this the the following expression:

const joinItems = (items = []) => items?.join(', ') ?? '';

console.log(joinItems(['Hello', 'World'])); // "Hello, World"
console.log(joinItems());                   // ""

return "" will return an empty string. If the function is returning undefined, there's something else wrong with your function.

function fn () {
  return "";
}
console.log(typeof fn());
// 'string'

function check(param){
    if (param.length == 0){
        return "";
    }
}

console.log(check([]));

Works fine for me, check if the array is empty by checking if the length is 0. You are getting undefined because your ' return "" ' line is not being run.

You need to check that your input is an array, then check that its length is 0.

function checkArrayIsEmpty(arr) {
    if(Array.isArray(arr) && arr.length === 0) {
        return "";
    } else {
        return "not an empty array";
    }
}

if (strs.length==1)
  return strs[0]

This worked for me.