Basically, I'm trying to figure out what the difference is between these 3 statements? Is there any reason to use one instead of the others? Is the first one bad practice (it works but I never see it and doesn't seem to be taught anywhere)?
+'21';
Number('21');
parseInt('21');
parseInt parses the string up to the first non-digit number and returns what it found,
For example: parseInt('123abc') // returns 123;
Number tries to convert the entire string into a number if it can.
ForExample: Number('123abc') // returns NaN
Unary plus operator can also be used to convert a string into a number, but it is not very readable when it is being used with other expressions and operators
Internally, +'21' will work in the same way as Number('21') * 1
As far as I know the first two are completely equivalent, and the choice between them is a matter of taste. (Personally I prefer the unary + because it's more concise, and well understood by most JS developers.)
parseInt is different because it reads a number value from the start of the string and ignores the rest when it reaches a non-numeric character. A common use is getting the underlying number from a CSS value like "20px". Note that the other two methods would fail with a NaN in this case.
Numberstands out. But if you have something likereturn +resultthat should be fine. A unary plus is idiomatic but I personally preferNumberfor conversions because it's easier to see and you can also use it in something like["1", "2", "3"].map(Number)