forEach中的箭头函数中的三元运算符

Question

I have this little function that is supposed to remove object properties with even values.

function removeEvenValues(obj) {
  Object.keys(obj).forEach(k => ((!isNaN(obj[k])) && (obj[k] % 2 === 0)) ? delete obj[k] : k);
}

In the else {} part of the ternary operator, how do I leave it empty like in an if (true){ doSomething();} kind of construct? Or does it even make sense to use a fat arrow function in this case?

Answer 1

Yes, you shouldn't use a concise arrow function or a ternary operator here. Well, you could use && instead of the ternary , but you really shouldn't.

You shouldn't even use forEach in ES6 - just use a proper loop:

function removeEvenValues(obj) {
  for (const k of Object.keys(obj))
    if (!isNaN(obj[k]) && obj[k] % 2 === 0)
      delete obj[k];
}

or (as you probably don't care about inherited properties)

function removeEvenValues(obj) {
  for (const k in obj)
    if (!isNaN(obj[k]) && obj[k] % 2 === 0)
      delete obj[k];
}

Answer 2

There is nothing wrong with using a fat arrow, as it is a function expression, but because you are not returning a value, you shouldn't use a ternary operator. You can do:

function removeEvenValues(obj) {
    Object.keys(obj).forEach(k => {if(!isNaN(obj[k]) && (obj[k] % 2 === 0)) {delete obj[k]}});
}

Answer 3

You could use a logical AND && and remove some superfluous parentheses.

 function removeEvenValues(obj) { Object.keys(obj).forEach(k => !isNaN(obj[k]) && obj[k] % 2 === 0 && delete obj[k]); } var o = { foo: 41, bar: 42 }; removeEvenValues(o); console.log(o); 

Answer 4

As Nina wrote, you can use logical operators instead of the ternary operator. You can also turn the condition around and use || .

Be aware though what isNaN returns. For instance isNaN([2]) === false ! So instead you might want to test for the primitive number type with typeof .

Finally, recently the Object.entries method has found its way in some browsers, and in this case it can be nice to use instead of Object.keys :

 function removeEvenValues(o) { Object.entries(o).forEach(([k, v]) => typeof v != "number" || v % 2 || delete o[k]); } // Sample var obj = { "a": 2, "b": "hello", "c": [4], "d": 5, "e": 6 }; removeEvenValues(obj); console.log(obj);