如何摆脱该函数的第一个if语句？

Question

I am writing a function that checks if an input is even or not. There are some preset conditions for what it must output, for example both the number 42 and string "42" should read as even. Here is the code I have:

function isEven (inputEven) {
  if (inputEven === false) {
    return false;
  }
  else {
    inputEven = Number(inputEven);
    if (inputEven%2 === 0) {
      return true;
    }
    else {
      return false;
    }
  }
}

As you can see at the start of the function I have an if statement to check if the input is the boolean false. I had to do this as if my function is given that without that if statement it will give back true while my requirement sheet says it needs to give back false. Is there any way to simplify this down to a single if/else statement?

Answer 1

try using parseInt instead.

 function isEven (inputEven) { var val = parseInt(inputEven, 10); return (!isNaN(val) && val%2 === 0); } console.log('empty', isEven()); console.log("''", isEven('')); console.log('true', isEven(true)); console.log('false', isEven(false)); console.log("'dogs'", isEven('dogs')); console.log("'true'", isEven('true')); console.log("'false'", isEven('false')); console.log('0', isEven(0)); console.log('1', isEven(1)); console.log('2', isEven(2)); console.log("'3'", isEven('3')); console.log("'4'", isEven('4')); 

Answer 2

Your function returns true for an empty string. You wrote in comments that it should in fact return false in that case. So I had to update my answer after getting that info:

But first: it is almost never needed to have a pattern like this:

if (something) {
    return true;
} else {
    return false;
}

You can just return the value of something in that case, possibly converted to boolean.

In your case all can be brought down to the following:

function isEven(inputEven) {
    return inputEven !== false && inputEven !== "" && (Number(inputEven)%2===0);
}

Answer 3

I ended up using:

function isEven (inputEven) {
  return parseFloat(inputEven)%2 === 0;
}

Which meets all of the requirements for the test script.