JavaScript regex.exec() should intended to use an assembled regEx

September 28, 2022

if I use ( https://jsfiddle.net/fgsvzn4a/ ) :

var text = "ui1pu";
var regExParameter = '\d+';
var regEx = '/(.*)' + regExParameter + '(.*)/gi';
var matches = regEx.exec(text);
if(matches && matches[1]) {
    var str1 = matches[1];
    var str2 = matches[2];
    var newStr = str1 + str2
    console.log(newStr);
}

i get this error:

Paused on exception
TypeError: regEx.exec is not a function

this prototype is working (inspired by https://stackoverflow.com/a/15845184/2891692 ):

var text = "my1bla";
var matches = /(my)\d+(.*)/gi.exec(text);
if(matches && matches[1]) {
var str1 = matches[1];
var str2 = matches[2];
var newStr = str1 + str2
alert(newStr);
}

but i want to use input parameters to build the regex (first example).

i get ReferenceError: Regex is not defined if i try this:

var text = "ui1pu";
var regExParameter = '\d+';
var regExString = '/(.*)' + regExParameter + '(.*)/gi';
var regEx = new Regex(regExString);
var matches = regEx.exec(text);
if(matches && matches[1]) {
    var str1 = matches[1];
    var str2 = matches[2];
    var newStr = str1 + str2
    console.log(newStr);
}

any idea?

>Solution :

Use the RegExp constructor. Note that the slashes should be omitted from the string and the flags should be passed as the second argument.

var text = "ui1pu";
var regExParameter = '\\d+';
var regExString = '(.*)' + regExParameter + '(.*)';
var regEx = new RegExp(regExString, 'gi');
var matches = regEx.exec(text);
if(matches && matches[1]) {
    var str1 = matches[1];
    var str2 = matches[2];
    var newStr = str1 + str2
    console.log(newStr);
}