How to use RegEx with String.Replace() in JavaScript

Regular Expressions (also called RegEx or RegExp) are a powerful way to analyze text. With RegEx, you can match strings at points that match specific characters (for example, JavaScript) or patterns (for example, NumberStringSymbol - 3a&).

The .replace method is used on strings in JavaScript to replace parts of string with characters. It is often used like so:

const str = 'JavaScript';
const newStr = str.replace("ava", "-");
console.log(newStr);
// J-Script

As you can see above, the replace method accepts two arguments: the string to be replaced, and what the string would be replaced with.

Here is where Regex comes in.

The use of .replace above is limited: the characters to be replaced are known - “ava”. What if we’re concerned with a pattern instead? Maybe, a number, two letters, and the word “foo” or three symbols used together?

The .replace method used with RegEx can achieve this. RegEx can be effectively used to recreate patterns. So combining this with .replace means we can replace patterns and not just exact characters.

How to use RegEx with .replace in JavaScript

To use RegEx, the first argument of replace will be replaced with regex syntax, for example /regex/. This syntax serves as a pattern where any parts of the string that match it will be replaced with the new substring.

Here’s an example:

// matches a number, some characters and another number
const reg = /\d.*\d/
const str = "Java3foobar4Script"
const newStr = str.replace(reg, "-");
console.log(newStr);
// "Java-Script"

The string 3foobar4 matches the regex /\d.*\d/, so it is replaced.

What if we wanted to perform replacements at multiple places?

Regex already offers that with the g (global) flag, and the same can be used with replace. Here’s how:

const reg = /\d{3}/g
const str = "Java323Scr995ip4894545t";
const newStr = str.replace(reg, "");
console.log(newStr);
// JavaScrip5t
// 5 didn't pass the test :(

The regex matches parts of the string that are exactly 3 consecutive numbers. 323 matches it, 995 matches it, 489 matches it, and 454 matches it. But the last 5 does not match the pattern.

The result is that JavaScrip5t shows how the patterns are correctly matched and replaces with the new substring (an empty string).

The case flag - i can also be used. This means you can replace case-insensitive patterns. Here’s how it is used:

const reg1 = /\dA/
const reg2 = /\dA/i
const str = "Jav5ascript"
const newStr1 = str.replace(reg1, "--");
const newStr2 = str.replace(reg2, "--");
console.log(newStr1) // Jav5ascript
console.log(newStr2) // Jav--script

..5a.. does not match the first syntax because RegEx is by default case-sensitive. But with the usage of the i flag, as seen in the second syntax, the string is as expected - replaced.

#javascript #regex #programming #developer #web-development

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How to use RegEx with String.Replace() in JavaScript
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JavaScript Regex Match Example – How to Use JS Replace on a String

Developers have been using text editors for a long time. And like most tools, all text editors have one feature in common: find and replace.

If you have been using find and replace for a while, you might know how useful this feature is. But most of us don’t know that this tool is even more powerful than we realize.

It can not only replace plain strings, but patterns too. These patterns are known as Regular Expressions.

Regular expressions exist in JavaScript and most other programming languages. Regex (for short) are a very powerful tool to help you find simple as well as complex search patterns.

String-searching algorithms are also a significant branch of computer science. In this article we will learn how to use this amazing tool in JavaScript.

Why Regular Expressions?

You won’t understand the real importance of Regular expressions until you are given a long document and are told to extract all emails from it.

You could do that manually, but there is a super fast method that can do it for you. Most modern text editors allow Regex in their Find option. It is usually denoted by .*.

Extracting Emails using Regex

And that’s not all regex can do – emails are just an example. You could search any type of string that follows a pattern, for example URLs or text between parentheses.

Regex can also be used to validate certain types of patterns, like validating Email. You could replace some long validation logic like this:

function IsValidEmail(email) {
        if (email.length <= 2) {
            return false;
        }

        if (email.indexOf("@") == -1) {
            return false;
        }

        var parts = email.split("@");
        var dot = parts[1].indexOf(".");
        var len = parts[1].length;
        var dotSplits = parts[1].split(".");
        var dotCount = dotSplits.length - 1;

        if (dot == -1 || dot < 2 || dotCount > 2) {
            return false;
        }

        for (var i = 0; i < dotSplits.length; i++) {
            if (dotSplits[i].length == 0) {
                return false;
            }
        }

        return true;
    };

#javascript #regex #developer #string

Javascript String Replace: How to Replace String in JavaScript

Javascript String replace() is an inbuilt function that returns the new string with some or all matches of the pattern replaced by the replacement. The pattern can be the string or the RegExp or Regular Expression, and the replacement can be the string or the function to be called for each match. If the pattern is a  string, only the first occurrence will be replaced.

Javascript String replace()

The javascript string replace() method does not change the String object it is called on. It only returns a new string if we want to perform a global search and replace, including the g switch in the regular expression.

Syntax

The syntax of the Javascript string replace() method is the following.

string.replace(searchValue, newValue)

#javascript #javascript string replace #regexp #regular expression

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How to use RegEx with String.Replace() in JavaScript

Regular Expressions (also called RegEx or RegExp) are a powerful way to analyze text. With RegEx, you can match strings at points that match specific characters (for example, JavaScript) or patterns (for example, NumberStringSymbol - 3a&).

The .replace method is used on strings in JavaScript to replace parts of string with characters. It is often used like so:

const str = 'JavaScript';
const newStr = str.replace("ava", "-");
console.log(newStr);
// J-Script

As you can see above, the replace method accepts two arguments: the string to be replaced, and what the string would be replaced with.

Here is where Regex comes in.

The use of .replace above is limited: the characters to be replaced are known - “ava”. What if we’re concerned with a pattern instead? Maybe, a number, two letters, and the word “foo” or three symbols used together?

The .replace method used with RegEx can achieve this. RegEx can be effectively used to recreate patterns. So combining this with .replace means we can replace patterns and not just exact characters.

How to use RegEx with .replace in JavaScript

To use RegEx, the first argument of replace will be replaced with regex syntax, for example /regex/. This syntax serves as a pattern where any parts of the string that match it will be replaced with the new substring.

Here’s an example:

// matches a number, some characters and another number
const reg = /\d.*\d/
const str = "Java3foobar4Script"
const newStr = str.replace(reg, "-");
console.log(newStr);
// "Java-Script"

The string 3foobar4 matches the regex /\d.*\d/, so it is replaced.

What if we wanted to perform replacements at multiple places?

Regex already offers that with the g (global) flag, and the same can be used with replace. Here’s how:

const reg = /\d{3}/g
const str = "Java323Scr995ip4894545t";
const newStr = str.replace(reg, "");
console.log(newStr);
// JavaScrip5t
// 5 didn't pass the test :(

The regex matches parts of the string that are exactly 3 consecutive numbers. 323 matches it, 995 matches it, 489 matches it, and 454 matches it. But the last 5 does not match the pattern.

The result is that JavaScrip5t shows how the patterns are correctly matched and replaces with the new substring (an empty string).

The case flag - i can also be used. This means you can replace case-insensitive patterns. Here’s how it is used:

const reg1 = /\dA/
const reg2 = /\dA/i
const str = "Jav5ascript"
const newStr1 = str.replace(reg1, "--");
const newStr2 = str.replace(reg2, "--");
console.log(newStr1) // Jav5ascript
console.log(newStr2) // Jav--script

..5a.. does not match the first syntax because RegEx is by default case-sensitive. But with the usage of the i flag, as seen in the second syntax, the string is as expected - replaced.

#javascript #regex #programming #developer #web-development