CODEWITHSUNDEEP
javascript
Govind Rai
Govind Rai

Reputation: 15830

Function returns empty array instead of arguments object when called inside of another method

Here's a simple function I invented to test out JavaScript's argument object versus rest parameters.

function f(a, b, ...theArgs) { 
  console.log(theArgs); 
  console.log(arguments); 
  return arguments;
}

if I call this function, say with these parameters: f(1,2,6,5,8,9,10,'a') I'll get two console logs and then the argument objects is returned. All great.

However, if I pass this function to: Array.prototype.slice(f(1,2,6,5,8,9,10,'a'), f.length), I will get an empty array back instead of an array like [6,5,8,9,10,'a']-- it appears that in this case my function is returning an empty array instead of the arguments object.

Why is that? Here's a snapshot of my console:

enter image description here

Upvotes: 0

Views: 333

Answers (1)

castletheperson
castletheperson

Reputation: 33496

Array.prototype is the empty array that your code is slicing on, not the result of f.

The first parameter to slice must be a number. In your code, f returns an object. If you want to change the this value of the slice function so that it slices your object instead, use .call:

Array.prototype.slice.call(f(1, 2, 6, 5, 8, 9, 10, 'a'), f.length)


function f(a, b, ...theArgs) {
  //console.log(theArgs);
  //console.log(arguments);
  return arguments;
}

console.log(Array.prototype.slice.call(f(1, 2, 6, 5, 8, 9, 10, 'a'), f.length));

Upvotes: 1

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