How do you use a variable in a regular expression?

How to escape and not to be awkward at parties

Reality check: special characters in regex context are misunderstood souls (. ? * + | ( )) - make them feel at home by escaping them:

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // Because comfort zones are cozy
}

let term = 'example.';
let safeTerm = escapeRegExp(term);
let regex = new RegExp(safeTerm, 'g'); // Escapism champion: /example\./g
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Feeling global? Slap in the g flag and replace every instance:

let content = 'An example with another example.';
let newContent = content.replace(regex, 'test'); // No more examples. Only tests here.
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Substitution, because who doesn't love a good switcheroo:

let price = 'Prices start at $3.99';
let currency = '\\$';
let regex = new RegExp(currency, 'g');
price = price.replace(regex, '€'); // Initial '$' was so mainstream...
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With syntax nuisances, remember: constructor syntax (new RegExp) takes charge when your patterns are dynamic divas.

Why regex when you can just...not

For over-simple replacements, Regex might as well be a hammer for a thumbtack:

let greeting = 'Hello, Jane!';
greeting = greeting.split('Jane').join('John'); // Jane who? 
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This replaces names without needing a complex formula. Simple wins.

Regex: The Masterclass

Embed your variable within a context in your regex. It's like engraving initials on a ring:

let prefix = 'User';
let regex = new RegExp(`\\b${prefix}\\d{2}\\b`, 'g'); // Bounty hunting 'User' with any two numbers as companions.
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Here, template literals and double backslashes are like mints and lip balm on a date – setting up the right context.

Case-insensitive searches need the gentler 'i' flag:

let insensitiveSearch = new RegExp(variable, 'gi');
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Examples and pitfalls – the good, the bad, the ugly

Validating inputs with regex

Double-check when validating user input, like an email, with regex. Because regex isn't a swiss army knife:

let emailPattern = /^[\w.-]+@[a-zA-Z\d.-]+\.[a-zA-Z]{2,6}$/;
let email = userInput;
let emailRegex = new RegExp(emailPattern);
let isValid = emailRegex.test(email); // Cousin to the immigration officer
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Dynamic pattern building

Dynamic patterns are unpredictable like weather: here, RegExp syntax dons the weatherman's hat:

let basePattern = 'file';
let dynamicPart = '2023'; // Because we're so future
let fullPattern = `${basePattern}_${dynamicPart}`;
let regex = new RegExp(fullPattern);
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The escape artist

A literal backslash in your pattern \\ is as elusive and chilling as the 'He who must not be named'. Whip the sorcery out:

let filePath = 'C:\\Documents\\Reports';
let cleanPath = filePath.replace(new RegExp('\\\\', 'g'), '/'); // Your path, your rules
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