Javascript Regex How to put a variable inside a regular expression

Question

So for example   function input       var testVar   input      string           string replace  ReGeX   testVar   ReGeX    replacement       But this is of course not working    Is there any way to do this

User · Answer

To build a regular expression from a variable in JavaScript, you'll need to use the RegExp constructor with a string parameter.

function reg(input) {
    var flags;
    //could be any combination of 'g', 'i', and 'm'
    flags = 'g';
    return new RegExp('ReGeX' + input + 'ReGeX', flags);
}

of course, this is a very naive example. It assumes that input is has been properly escaped for a regular expression. If you're dealing with user-input, or simply want to make it more convenient to match special characters, you'll need to escape special characters:

function regexEscape(str) {
    return str.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')
}

function reg(input) {
    var flags;
    //could be any combination of 'g', 'i', and 'm'
    flags = 'g';
    input = regexEscape(input);
    return new RegExp('ReGeX' + input + 'ReGeX', flags);
}

User · Answer

Here s an pretty useless function that return values wrapped by specific characters      jsfiddle  https   jsfiddle net squadjot 43agwo6x   function getValsWrappedIn str c1 c2       var rg   new RegExp     lt      c1               c2      g         return str match rg          var exampleStr    Something  5  or some time  19  or maybe a  thingy    var results    getValsWrappedIn exampleStr              Will return array   5   19   thingy   console log results

User · Answer

You can always give regular expression as string  i e   ReGeX    testVar    ReGeX   You ll possibly have to escape some characters inside your string  e g   double quote   but for most cases it s equivalent   You can also use RegExp constructor to pass flags in  see the docs

User · Answer

It s only necessary to prepare the string variable first and then convert it to the RegEx   for example   You want to add minLength and MaxLength with the variable to RegEx   function getRegEx         const minLength    5      for exapmle  min is 5     const maxLength    12      for exapmle  man is 12      var regEx           minLength        maxLength           first we make a String variable of our RegEx     regEx   new RegExp regEx   g       now we convert it to RegEx      return regEx     In the end  we return the RegEx     now if you change value of MaxLength or MinLength  It will change in all RegExs   Hope to be useful  Also sorry about my English

User · Answer

accepted answer doesn t work for me and doesn t follow MDN examples  see the  Description  section in above link  I d go with the following it s working for me   let stringThatIsGoingToChange    findMe   let flagsYouWant    gi    simple string with flags let dynamicRegExp   new RegExp    stringThatIsGoingToChange    flagsYouWant      that makes dynamicRegExp    findMe gi

User · Answer

const regex   new RegExp  ReGeX  testVar ReGeX        string replace regex   replacement      Update  Per some of the comments  it s important to note that you may want to escape the variable if there is potential for malicious content  e g  the variable comes from user input   ES6 Update  In 2019  this would usually be written using a template string  and the above code has been updated  The original answer was   var regex   new RegExp  ReGeX    testVar    ReGeX        string replace regex   replacement

User · Answer

You can create regular expressions in JS in one of two ways     Using regular expression literal -  ab 2  g Using the regular expression constructor - new RegExp  ab 2     g        Regular expression literals are constant  and can not be used with variables  This could be achieved using the constructor  The stracture of the RegEx constructor is   new RegExp regularExpressionString  modifiersString    You can embed variables as part of the regularExpressionString  For example    var pattern  cd  var repeats 3 new RegExp    pattern    repeats      g      This will match any appearance of the pattern cdcdcd

User · Answer

You can use the RegExp object   var regexstring    whatever   var regexp   new RegExp regexstring   gi    var str    whateverTest   var str2   str replace regexp   other    document write str2     Then you can construct regexstring in any way you want    You can read more about it here

User · Answer

if you re using es6 template literals are an option     string replace new RegExp  ReGeX  testVar ReGeX     replacement

[javascript] Javascript Regex: How to put a variable inside a regular expression?

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