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

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

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?

Solutions/Answers:

Solution 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)

Solution 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.

Solution 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);
}

Solution 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.

Related:  How can I merge TypedArrays in JavaScript?

You can also use RegExp constructor to pass flags in (see the docs).

Solution 5:

if you’re using es6 template literals are an option…

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

Solution 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