为什么我的数组的最后一个元素被替换为0

Question

I have a function:

function splitToDigits(n) {
    var digits = ("" + n).split("").map(function(item) {
        return parseInt(item, 10);
    });
    console.log(digits);
}

console.log(splitToDigits(123456784987654321));

This is returning digits = [1,2,3,4,5,6,7,8,4,9,8,7,6,5,4,3,2,0] .

Any idea why the last element is 0 ? I noticed that when I delete 2 elements from the array it acts normally. Thanks for all the great answers! :)

Answer 1

As Jaromanda X mentioned in the comments section above, JavaScript does not have enough precision to keep track of every digit in the integer you passed to your function.

To fix this problem, you should instead pass a string:

console.log(splitToDigits('123456784987654321'))

However, I would also like to point out that you can greatly simplify your splitToDigits method:

 function splitToDigits(n) { return [].map.call(n + '', Number) } console.log(splitToDigits('123456784987654321')) console.log(splitToDigits(1234)) 

Answer 2

It's because Javascript is truncating numbers.

The best way to see this is by doing this console.log:

function splitToDigits(n) {
console.log(n);
var digits = ("" + n).split("").map(function(item) {
    return parseInt(item, 10);
});
}

Then, when you ran: splitToDigits(123456784987654321) , you already get 123456784987654320. Hence, it has nothing to do with your code as you have still not processed it.

If you add digits, it changes to scientific notation:

splitToDigits(1234567849876543211521521251) // turns to 1.2345678498765432e+27

It's a Javascript precision issue. That's all :)