Using variables in regular JavaScript

Question

Hello. Suppose there is such a pattern, a-zA-Zа-яёА-ЯЁ0-9\-\_ . I use it in match() regular expression

Here is the full regular expression:

 'AQwerty_083аСBlah-‌Blah-Blah'.match(/[a-zA-Zа-яёА-ЯЁ0-9\-\_]/gi); // оно вернёт: ["A", "Q", "w", "e", "r", "t", "y", "_", "0", "8", "3", "а", // "С", "B", "l", "a", "h", "-", "B", "l", "a", "h", "-", "B", "l", "a", "h"]

There are no problems with this. Further, in a special function, a template is formed, which is returned approximately in the following form: "a-zA-Zа-ЯЁА-ЯЁ0-9-_", as a string. Then I try to use this template in the regular schedule, like this:

 var tmp_rg = tmp_rg('eng+rus+fig+-+_'); // "a-zA-Zа-яёА-ЯЁ0-9\-\_" var regexp = /[tmp_rg]/gi; var matches = "AQwerty_083аСBlah-Blah-Blah".match(regexp); // возвратит: ["r", "t", "_"], т.к. не воспринимает переменную console.log(matches);

This is clear to me. But then I tried to put a variable through new RegExp(tmp, 'gi') into the regular routine itself. And wrote it like this:

 var tmp_rg = tmp_rg('eng+rus+fig+-+_'); // "a-zA-Zа-яёА-ЯЁ0-9\-\_" var matches = "AQwerty_083аСBlah-Blah-Blah".match(new RegExp(tmp_rg, 'gi')); // возвратит: null, ну а тут я не знаю в чем дело console.log(matches);

Explain to me people who know why this is happening? Why can't the variable be added to the regular? Already the 2nd week I suffer with these regulars.

tmp_rg() returns a string of the type [a-zA-Zа-яёА-ЯЁ0-9\-\_] or immediately RegExp?
Something is unclear as 'AQwerty_083аСBlah-Blah-Blah'.match(a-zA-Zа-яёА-ЯЁ0-9\-\_);
Must be 'AQwerty_083аСBlah-Blah-Blah'.match(/[a-zA-Zа-яёА-ЯЁ0-9_-]/g);
returns: "a-zA-Zа-яёА-ЯЁ0-9 \ -_" together with quotes
In general, you should not assign the value of a variable function whose name matches the function name: var tmp_rg = tmp_rg('eng+rus+fig+-+_');
@Grundy, if the function is at one time, then does it matter?
@ WiktorStribiżew, corrected, was originally written, as you wrote, like this: 'AQwerty_083аСBlah-‌Blah-Blah'.match(/[a-zA-Zа-яёА-ЯЁ0-9\-\_]/gi)

Wiktor Stribiżew Wiktor Stribiżew 11.8k 2 13 32 · Accepted Answer · 2016-08-17T12:47:53

Use the constructor to create a RegExp object from a variable:

 var tmp_rg = "a-zA-Zа-яёА-ЯЁ0-9\\-_"; var regexp = RegExp("[" + tmp_rg + "]", "gi"); var matches = "AQwerty_083аСBlah-Blah-Blah".match(regexp); console.log(matches);

Note that the sign does not have to be escaped at a given place or at the beginning or end of a character class; however, if the template needs to be changed later, it is safer to save the screening.

Character class - [...] - finds 1 character from the character sets and character ranges defined in it.

It is easy, if in tmp_rg all ranges and characters are specified as necessary, then what is needed is escaped (in the code with the help of two backslashes).
The underscore symbol _ never necessary to be escaped in any type of regulars.
I’m talking about something else, you needed less than 5 minutes to solve this problem, and I’m been tormenting it for several days.
If you know English, you can quickly learn the basics of RegexOne .
On the MDN website, you can find everything related to the implementation of regulars in JS, and on SO, such problems have long been described.
And here's another link to Wikibooks for regular expressions .
It is easy to test expressions on Regex101.com , and for JS there is also Regexr .

user207618 · Answer 2 · 2016-08-17T12:43:15

With the RegExp designer, everything is fine, but the regular is incorrect.
It is necessary to make a character class - [a-zA-Zа-яёА-ЯЁ0-9\-\_] .

Corrected, it was originally as follows: 'AQwerty_083аСBlah-‌‌Blah-Blah'.match(/[a‌-zA-Zа-яёА-ЯЁ0-9\-_]‌/gi)

Using variables in regular JavaScript

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