Given a variable str containing a string value, are these two lines of code equivalent?
Line A:
if ( [ 'foo', 'bar', 'baz' ].indexOf( str ) > -1 ) { Line B:
if ( /^foo|bar|baz$/.test( str ) ) { 
- possible duplicate of Is there a version of JavaScript's String.indexOf() that allows for regular expressions?Daniel A. White– Daniel A. White2011-11-27 03:09:02 +00:00Commented Nov 27, 2011 at 3:09
- 2Not quite a duplicate. He wants to convert indexOf to a regex, that question wants to call indexOf on a regex.Dan– Dan2011-11-27 03:11:32 +00:00Commented Nov 27, 2011 at 3:11
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3 Answers
Not quite. The pipes are including the ^ and $ as alternatives. I'm not entirely clear on the syntax of JS's regular expressions, but if you're looking for str to contain only foo, or bar, or baz, use the expression /^(foo|bar|baz)$/. If you're looking to do something different, let me know and I'll try to clear it up.
3 Comments
Šime Vidas
I would like to achieve the behavior of Line A with Line B. (So, yes, I want to check if
str is exactly one of those 3 values... )
Dan
Then yes, you want the regex I gave you. Alternately, if you don't need to capture /which/ value you match, you can use
/^(?:foo|bar|baz)$/. The ?: means 'don't bother remembering which one of these three matches', and it might be a bit fasterŠime Vidas
Could you explain why i have to group my
a|b|c? How does it make a difference?No, they are not.
The method indexOf() returns -1 if the item is not found in the array, or the position of the array if it is found in the array.
The method test returns true if the regex finds a match, and false if it doesn't.
If your regular expression was instead /^(foo|bar|baz)$/, then the function would be the same.
2 Comments
Šime Vidas
But why are the parens required?
Phrogz
@ŠimeVidas Because
/^foo|bar$/ is ^foo OR bar$, and thus would match "fools", and would also match "sandbar".Okay, after the edit, they're still not equivalent since test will call toString. See:
var myItem = {toString: function() { return 'foo'; }}; ['foo', 'bar', 'baz'].indexOf(myItem); // -1 /^(foo|bar|baz)$/.test(myItem); // true Even when they're string values (sorry, missed that) then they're still not equivalent because there are two different types of strings and indexOf uses strict equality/identity:
To make them truly equivalent, you can either call .toString() before using indexOf, or you can test Object.prototype.toString.call(myItem) === '[object String]' before using test.
7 Comments
Dan
Still they're different. Minitech gave you a few examples of things that B will catch that A will not, and see the regex I gave you for how to fix it.
Šime Vidas
@minitech Yes, but I mentioned in my question that
str is a string value... It can't be an object.
Ry-
@ŠimeVidas: Sorry, missed that. I edited my answer again - they're still not equivalent.
Šime Vidas
@minitech Uh...
:) When I said "string value", I meant a value of the String type, not a String object... (String objects are useless, I would never use them... ) |