Javascript Regex: How to put a variable inside a r

问题:

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?

回答1:

var 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)

回答2:

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.

回答3:

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);
}

回答4:

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).

回答5:

if you\'re using es6 template literals are an option...

string.replace(new RegExp(`ReGeX${testVar}ReGeX`), \"replacement\")

回答6:

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

回答7:

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(\"(?<=\\\\\"+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)

回答8:

You can create regular expressions in JS in one of two ways:

1. Using regular expression literal - /ab{2}/g
2. 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.