[].slice will create new object and Array.prototype.slice don't

Fair points, but it shouldn't be marked as "incorrect" since the requirements you've listed are not mentioned in the description.

This solution is attempting to use duck-typing, however it is a problematic approach because the length property could be added to an Object.

obj = {};
obj.length = 0;

obj.hasOwnProperty('length') // => true
obj.toString() // => "[object Object]"

This solution is attempting to use duck-typing, however it is a problematic approach because the length property could be added to an Object.

obj = {};
obj.length = 0;

obj.hasOwnProperty('length') // => true
typeof obj // => "[object Object]"

On top of that, you are using an if/else statement, when you could just return value.hasOwnProperty('length') (even though hasOwnProperty is not the best approach).

This solution is attempting to use duck-typing, however it is a problematic approach because the length property could be added to an Object.

obj = {};
obj.length = 0;

obj.hasOwnProperty('length') // => true
typeof obj // => "[object Object]"

Except that the description says to append "..." to the returned string, so you would have to check that limit+3 === returnValue.length.

I just tried to submit my solution and it failed me because it says solution("Test", 10) did not return "Test" even though my code was correct as described by the instructions.

Dropping curly braces in JavaScript is a bad practice. It can lead to unexpected behavior due to JavaScript auto-semicolon-insertion feature.

Consider the following:

function broken() 
{
  return
  {
    state: 'broken'
  }
}

// what would this output?
console.log(broken())

Dropping curly braces in JavaScript is a bad practice. It can lead to unexpected behavior due to JavaScript auto-semicolon-insertion feature.

Consider the following:

function broken() 
{
  return
  {
    state: 'broken'
  }
}

// what would this output?
console.log(broken())

Define the toString method by assigning it to the constructor's prototype.

It's better to throw an error here than assign empty strings if the right parameters are not given. How will you debug code like this?

Completely unmaintainable.