将扩展数组映射到数字

Question

When mapping an array containing integers and strings I want to cast only the numbers.

Assume the array ['55', 'abc'] is passed as a param to a function.

How can I use the spread operator and get the same results?

"Run code snippet" and notice that with the spread operator, 55 is not cast to a number.

 console.log(['55', 'abc'].map(val => isNaN(val) ? val : Number(val))) console.log(...[['55', 'abc']].map(val => isNaN(val) ? val : Number(val)))

Answer 1

How can I use the spread operator and get the same results?

You can't. Spread (which is syntax, not an operator) doesn't do mapping. It spreads out values. For mapping, stick with map (what you have in the first line of your code). (Or if you were starting with something that was just array-like without actually being an array, you might use Array.from passing in a mapping callback. But your starting point in your example is an actual array.)

The reason your second line doesn't work is that you're calling map on the outer array, which has an array in it, so val in the callback is that array. isNaN(['55, 'abc']) ends up being isNaN('55,abc') which is true because '55,abc' when converted to the number type is NaN . So the callback returns the inner array unchanged.

Your first line creates a new array with the values mapped the way you seem to want them to be mapped.

Answer 2

Looks like you aren't spreading it into a new array. The below gives the desired result.

 console.log(['55', 'abc'].map(val => isNaN(val) ? val : Number(val))) console.log([...['55', 'abc']].map(val => isNaN(val) ? val : Number(val)))