# Quantifiers +, *, ? and {n} Let's say we have a string like `+7(903)-123-45-67` and want to find all numbers in it. But unlike before, we are interested not in single digits, but full numbers: `7, 903, 123, 45, 67`. A number is a sequence of 1 or more digits `\d`. To mark how many we need, we need to append a *quantifier*. ## Quantity {n} The simplest quantifier is a number in curly braces: `pattern:{n}`. A quantifier is appended to a character (or a character class, or a `[...]` set etc) and specifies how many we need. It has a few advanced forms, let's see examples: The exact count: `{5}` : `pattern:\d{5}` denotes exactly 5 digits, the same as `pattern:\d\d\d\d\d`. The example below looks for a 5-digit number: ```js run alert( "I'm 12345 years old".match(/\d{5}/) ); // "12345" ``` We can add `\b` to exclude longer numbers: `pattern:\b\d{5}\b`. The range: `{3,5}`, match 3-5 times : To find numbers from 3 to 5 digits we can put the limits into curly braces: `pattern:\d{3,5}` ```js run alert( "I'm not 12, but 1234 years old".match(/\d{3,5}/) ); // "1234" ``` We can omit the upper limit. Then a regexp `pattern:\d{3,}` looks for sequences of digits of length `3` or more: ```js run alert( "I'm not 12, but 345678 years old".match(/\d{3,}/) ); // "345678" ``` Let's return to the string `+7(903)-123-45-67`. A number is a sequence of one or more digits in a row. So the regexp is `pattern:\d{1,}`: ```js run let str = "+7(903)-123-45-67"; let numbers = str.match(/\d{1,}/g); alert(numbers); // 7,903,123,45,67 ``` ## Shorthands There are shorthands for most used quantifiers: `+` : Means "one or more", the same as `{1,}`. For instance, `pattern:\d+` looks for numbers: ```js run let str = "+7(903)-123-45-67"; alert( str.match(/\d+/g) ); // 7,903,123,45,67 ``` `?` : Means "zero or one", the same as `{0,1}`. In other words, it makes the symbol optional. For instance, the pattern `pattern:ou?r` looks for `match:o` followed by zero or one `match:u`, and then `match:r`. So, `pattern:colou?r` finds both `match:color` and `match:colour`: ```js run let str = "Should I write color or colour?"; alert( str.match(/colou?r/g) ); // color, colour ``` `*` : Means "zero or more", the same as `{0,}`. That is, the character may repeat any times or be absent. For example, `pattern:\d0*` looks for a digit followed by any number of zeroes: ```js run alert( "100 10 1".match(/\d0*/g) ); // 100, 10, 1 ``` Compare it with `'+'` (one or more): ```js run alert( "100 10 1".match(/\d0+/g) ); // 100, 10 // 1 not matched, as 0+ requires at least one zero ``` ## More examples Quantifiers are used very often. They serve as the main "building block" of complex regular expressions, so let's see more examples. Regexp "decimal fraction" (a number with a floating point): `pattern:\d+\.\d+` : In action: ```js run alert( "0 1 12.345 7890".match(/\d+\.\d+/g) ); // 12.345 ``` Regexp "open HTML-tag without attributes", like `` or `

`: `pattern:/<[a-z]+>/i` : In action: ```js run alert( " ... ".match(/<[a-z]+>/gi) ); // ``` We look for character `pattern:'<'` followed by one or more English letters, and then `pattern:'>'`. Regexp "open HTML-tag without attributes" (improved): `pattern:/<[a-z][a-z0-9]*>/i` : Better regexp: according to the standard, HTML tag name may have a digit at any position except the first one, like `

`. ```js run alert( "

Hi!

".match(/<[a-z][a-z0-9]*>/gi) ); //

``` Regexp "opening or closing HTML-tag without attributes": `pattern:/<\/?[a-z][a-z0-9]*>/i` : We added an optional slash `pattern:/?` before the tag. Had to escape it with a backslash, otherwise JavaScript would think it is the pattern end. ```js run alert( "

Hi!

".match(/<\/?[a-z][a-z0-9]*>/gi) ); //

,

``` ```smart header="To make a regexp more precise, we often need make it more complex" We can see one common rule in these examples: the more precise is the regular expression -- the longer and more complex it is. For instance, for HTML tags we could use a simpler regexp: `pattern:<\w+>`. ...But because `pattern:\w` means any English letter or a digit or `'_'`, the regexp also matches non-tags, for instance `match:<_>`. So it's much simpler than `pattern:<[a-z][a-z0-9]*>`, but less reliable. Are we ok with `pattern:<\w+>` or we need `pattern:<[a-z][a-z0-9]*>`? In real life both variants are acceptable. Depends on how tolerant we can be to "extra" matches and whether it's difficult or not to filter them out by other means. ```