4 ms·

You'll love the output of ['1', '7', '11'].map(parseInt)

by dividuum 6y ago

jannes 6y ago
Number() only takes a single parameter. The correct version is: ['1', '7', '11'].map(Number)
- dahfizz 6y ago
  If only the language did anything at all to help you realize the wrong version is wrong and that this is somehow different.
- davidmurdoch 6y ago
  Careful with that: https://jakearchibald.com/2021/function-callback-risks/ https://jakearchibald.com/2021/function-callback-risks/ Using `Number` is probably safe because it'd break much of the web of it were changed. Also note that it is not equivalent to parseInt, as Number and parseInt apply different parsing rules.
  - dividuum 6y ago
    Thanks for linking that post. I meant to include it in my comment but wasn't able to find it again.
pmontra 6y ago
One would assume it to be equivalent to (written in the most old style possible way so everybody can understand it) ['1', '7', '11'].map(function(n) {return parseInt(n);}) but no, map has got an extra argument, the index of the array function traceParseInt(n, i) { console.log(i); return parseInt(n, i); } ['1', '7', '11'].map(traceParseInt) 0 1 2 [ 1, NaN, 3 ] Nice way to wait for an integration test to complete. Thanks.
- erichocean 6y ago
  And parseInt() also take an extra argument, the "base" of the number—hence the weird results. (Which also means that a static type checker would not have caught this "bug".)
nobleach 6y ago
I've always found this example so frustrating. JavaScript isn't curried. Plenty of languages are not. `parseInt` is overloaded/variadic. What we know is if one does not read the documentation for `parseInt`, they might get unexpected results... but who's fault is that? I don't see this a a "hidden gotcha". Yes, if you came from say.... Pascal, and you were used to `StrToInt` taking one arg, and you refused to check into it, you'd get odd results. But who among us, when learning a new language don't look up things like, "how to convert a string to an integer in <insert name of new language>"? That search will most likely land you at some docs that explain that second arg.

You'll love the output of ['1', '7', '11'].map(parseInt)

jannes 6y ago

Number() only takes a single parameter. The correct version is: ['1', '7', '11'].map(Number)

dahfizz 6y ago
If only the language did anything at all to help you realize the wrong version is wrong and that this is somehow different.
davidmurdoch 6y ago
Careful with that: https://jakearchibald.com/2021/function-callback-risks/ https://jakearchibald.com/2021/function-callback-risks/ Using `Number` is probably safe because it'd break much of the web of it were changed. Also note that it is not equivalent to parseInt, as Number and parseInt apply different parsing rules.
- dividuum 6y ago
  Thanks for linking that post. I meant to include it in my comment but wasn't able to find it again.

pmontra 6y ago

One would assume it to be equivalent to (written in the most old style possible way so everybody can understand it) ['1', '7', '11'].map(function(n) {return parseInt(n);}) but no, map has got an extra argument, the index of the array function traceParseInt(n, i) { console.log(i); return parseInt(n, i); } ['1', '7', '11'].map(traceParseInt) 0 1 2 [ 1, NaN, 3 ] Nice way to wait for an integration test to complete. Thanks.

erichocean 6y ago
And parseInt() also take an extra argument, the "base" of the number—hence the weird results. (Which also means that a static type checker would not have caught this "bug".)

nobleach 6y ago

I've always found this example so frustrating. JavaScript isn't curried. Plenty of languages are not. `parseInt` is overloaded/variadic. What we know is if one does not read the documentation for `parseInt`, they might get unexpected results... but who's fault is that? I don't see this a a "hidden gotcha". Yes, if you came from say.... Pascal, and you were used to `StrToInt` taking one arg, and you refused to check into it, you'd get odd results. But who among us, when learning a new language don't look up things like, "how to convert a string to an integer in <insert name of new language>"? That search will most likely land you at some docs that explain that second arg.