String To Number Confusion

Question

Why does parseInt("-1000-500-75-33") return -1000?

Shouldn't it return the sum of those numbers: -1608

How can I get the string "-1000-500-75-33" to return as the sum of those numbers?

Answer 1

parseInt will try to get a number starting from the beginning of the string.

Since - is a valid character to begin a number with, it parses the string until it finds something invalid. The second - is invalid because no integer can contain an - inside it, only digits. So it stops there and considers the number to be "finished".

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Now, if you want to process the expression, you can use eval like so:

eval("-1000-500-75-33")

This will return -1608 as expected.

Answer 2

parseInt will not perform any computations, rather it will try to convert a string into an integer. It returns -1000 because the dash afterwards would not be considered a valid number. If you want to sum all these numbers you could split on the dash, map to Number, then reduce:

var numString = "-1000-500-75-33";
numString.split('-').map(e => Number(e)).reduce((a, b) => a - b);

Answer 3

Since they are in a string, ParseInt does not parse the whole string, just finds the first applicable number from the start & returns it. If the start of the string cannot be parsed, it returns NaN

parseInt("-1000NOT_NUMBER") = -1000
parseInt("test-1000`) = NaN

You have to use eval function to do what you want, that evaluates given string as if it were a command entered into the console;

eval("-1000-500-75-33") = -1608

Answer 4

Try to eval! it's safe here

eval("-1000-500-75-33").toString()

Answer 5

console.log(eval("-1000-500-75-33").toString());

And about type casting: After parsing -1000, which is obviously "negative 1000", It will escape casting as soon as it detect a symbol common between numbers & strings. So parseInt is seeing "-1000-500-75-33" as "-1000NotConvertableString", So left the remaining away, returning -1000 as the result of type-casting.