为什么 Number() function 在我这样使用时不起作用？

Question

 function sumDigits(num) { // your code here let nums = num.toString(); let sum = 0; for(let i = 0;i<nums.length;i++){ Number(nums[i]); console.log(typeof nums[i]); sum += nums[i]; } return sum; } var output = sumDigits(1148); console.log(output); // --> 14

Can someone explain why Number(nums[i]) does not change the type of the variable. Or any other way to solve this problem? The function is supposed to take in an integer value and add all the digits and return an integer.

When I tried to run the code i couldn't get the string to convert back into a number and would just add the value of sums to the front of the string.

Answer 1

You are not saving the value returned by Number(nums[i]) . But since here you are not using it more than once, you can just add it to the sum without assigning it to a variable.

 function sumDigits(num) { // your code here let nums = num.toString(); let sum = 0; for (let i = 0; i < nums.length; i++) { sum += Number(nums[i]); } return sum; } var output = sumDigits(1148); console.log(output); // --> 14

Answer 2

Number does not change the value it's used on. (It couldn't when used on a string, anyway, since strings in JavaScript are immutable.) It just returns a number. So you have to use that return value.

Try this instead:

for(let i = 0; i < nums.length; i++){
    sum += Number(nums[i]);
}

Answer 3

To fix your code, change sum += nums[i]; to sum += Number(nums[i]); . Reason: When you add a string to a number, the number is first converted to a string, and a string concatenation is performed.

Here is a functional programming approach to your question:

 function sumDigits(num) { return num.toString() // convert number to string.split('') // split into array of chars.reduce((acc, val) => { // reduce array to sum of items return acc + Number(val) }, 0); } var output = sumDigits(1148); console.log(output); // --> 14

Functional programming makes code more extensible, modular, reusable, performing, and testable.

Into to functional programming in JavaScript: https://opensource.com/article/17/6/functional-javascript

.reduce() docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce

Here is the same with a map reduce approach:

 function sumDigits(num) { return num.toString() // convert number to string.split('') // split into array of chars.map(char => Number(char)) // change each char in array to number.reduce((acc, val) => { // reduce array to sum of items return acc + val }, 0); } var output = sumDigits(1148); console.log(output); // --> 14

Intro to map reduce: https://medium.com/poka-techblog/simplify-your-javascript-use-map-reduce-and-filter-bd02c593cc2d