D3 Examples - // source http://jsbin.com/ginoqot

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<script id="jsbin-javascript">
// We’ve seen that % (the remainder operator) can be used to test whether a number is even or odd by using % 2 to check whether it’s divisible by two. Here’s another way to define whether a positive whole number is even or odd:
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// Zero is even.
​
// One is odd.
​
// For any other number N, its evenness is the same as N - 2.
​
// Define a recursive function isEven corresponding to this description. The function should accept a number parameter and return a Boolean.
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// Test it on 50 and 75. See how it behaves on -1. Why? Can you think of a way to fix this?
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// URL: https://eloquentjavascript.net/03_functions.html#p_iDq2OgBOGw
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function isEven(num) {
  
  num = Math.abs(num);
  
  if (num === 0) {
    return true;
  } else if (num === 1) {
    return false;
  }
  
  return isEven(num-2);
  
}
​
console.log(isEven(50));
console.log(isEven(75));
console.log(isEven(-1));
console.log(isEven(-100));
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<script id="jsbin-source-javascript" type="text/javascript">// We’ve seen that % (the remainder operator) can be used to test whether a number is even or odd by using % 2 to check whether it’s divisible by two. Here’s another way to define whether a positive whole number is even or odd:
​
// Zero is even.
​
// One is odd.
​
// For any other number N, its evenness is the same as N - 2.
​
// Define a recursive function isEven corresponding to this description. The function should accept a number parameter and return a Boolean.
​
// Test it on 50 and 75. See how it behaves on -1. Why? Can you think of a way to fix this?
​
// URL: https://eloquentjavascript.net/03_functions.html#p_iDq2OgBOGw
​
function isEven(num) {
  
  num = Math.abs(num);
  
  if (num === 0) {
    return true;
  } else if (num === 1) {
    return false;
  }
  
  return isEven(num-2);
  
}
​
console.log(isEven(50));
console.log(isEven(75));
console.log(isEven(-1));
console.log(isEven(-100));</script></body>
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