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JavaScript

Posted by Eric Flowers
Eric Flowers
9,472 Points

Basic question about parameters

This is from a challenge on another site, but my question is about programming.

How does JavaScript know what the parameter "a" is? Is there code missing here when "a" is defined by the user, say by .prompt()?

var puzzlers = [
  function ( a ) { return 3*a - 8; }, 
  function ( a ) { return (a+2) * (a+2) * (a+2); }, 
  function ( a ) { return a * a - 9; },
  function ( a ) { return a % 4; }
];

1 Answer

Michael Hulet
Michael Hulet
47,913 Points

a is defined when the function is called. The syntax in this case would look like this:

puzzlers[0](3);

That would call the first function in the array, and set a to 3. So 3 would be multiplied by 3, and 8 would be subtracted from the result, and the answer, in this case, would be 9. In this particular array, you could call any of the functions by replacing the 0 in my example with any number 0 - 3, and you could replace 3 with anything you want, and it will be assigned to a. The following example calls the 3rd function in the array and assigns a to 8:

puzzlers[2](8);

As previously stated, that code would call the 3rd function in the array, and assign a to 8, so 8 would be multiplied by 8 and 9 would be subtracted from the product, so the function would evaluate to 55.