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

What is GEEK

Buddha Community

JavaScript Regex Match Example – How to Use JS Replace on a String

NBB: Ad-hoc CLJS Scripting on Node.js

Nbb

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Status

Experimental. Please report issues here.

Goals and features

Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.

Additional goals and features are:

  • Fast startup without relying on a custom version of Node.js.
  • Small artifact (current size is around 1.2MB).
  • First class macros.
  • Support building small TUI apps using Reagent.
  • Complement babashka with libraries from the Node.js ecosystem.

Requirements

Nbb requires Node.js v12 or newer.

How does this tool work?

CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).

Usage

Install nbb from NPM:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'
6

And then install some other NPM libraries to use in the script. E.g.:

$ npm install csv-parse shelljs zx

Create a script which uses the NPM libraries:

(ns script
  (:require ["csv-parse/lib/sync$default" :as csv-parse]
            ["fs" :as fs]
            ["path" :as path]
            ["shelljs$default" :as sh]
            ["term-size$default" :as term-size]
            ["zx$default" :as zx]
            ["zx$fs" :as zxfs]
            [nbb.core :refer [*file*]]))

(prn (path/resolve "."))

(prn (term-size))

(println (count (str (fs/readFileSync *file*))))

(prn (sh/ls "."))

(prn (csv-parse "foo,bar"))

(prn (zxfs/existsSync *file*))

(zx/$ #js ["ls"])

Call the script:

$ nbb script.cljs
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs

Macros

Nbb has first class support for macros: you can define them right inside your .cljs file, like you are used to from JVM Clojure. Consider the plet macro to make working with promises more palatable:

(defmacro plet
  [bindings & body]
  (let [binding-pairs (reverse (partition 2 bindings))
        body (cons 'do body)]
    (reduce (fn [body [sym expr]]
              (let [expr (list '.resolve 'js/Promise expr)]
                (list '.then expr (list 'clojure.core/fn (vector sym)
                                        body))))
            body
            binding-pairs)))

Using this macro we can look async code more like sync code. Consider this puppeteer example:

(-> (.launch puppeteer)
      (.then (fn [browser]
               (-> (.newPage browser)
                   (.then (fn [page]
                            (-> (.goto page "https://clojure.org")
                                (.then #(.screenshot page #js{:path "screenshot.png"}))
                                (.catch #(js/console.log %))
                                (.then #(.close browser)))))))))

Using plet this becomes:

(plet [browser (.launch puppeteer)
       page (.newPage browser)
       _ (.goto page "https://clojure.org")
       _ (-> (.screenshot page #js{:path "screenshot.png"})
             (.catch #(js/console.log %)))]
      (.close browser))

See the puppeteer example for the full code.

Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet macro is similar to promesa.core/let.

Startup time

$ time nbb -e '(+ 1 2 3)'
6
nbb -e '(+ 1 2 3)'   0.17s  user 0.02s system 109% cpu 0.168 total

The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx this adds another 300ms or so, so for faster startup, either use a globally installed nbb or use $(npm bin)/nbb script.cljs to bypass npx.

Dependencies

NPM dependencies

Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.

Classpath

To load .cljs files from local paths or dependencies, you can use the --classpath argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs relative to your current dir, then you can load it via (:require [foo.bar :as fb]). Note that nbb uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar in the namespace name becomes foo_bar in the directory name.

To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:

$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"

and then feed it to the --classpath argument:

$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]

Currently nbb only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar files will be added later.

Current file

The name of the file that is currently being executed is available via nbb.core/*file* or on the metadata of vars:

(ns foo
  (:require [nbb.core :refer [*file*]]))

(prn *file*) ;; "/private/tmp/foo.cljs"

(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"

Reagent

Nbb includes reagent.core which will be lazily loaded when required. You can use this together with ink to create a TUI application:

$ npm install ink

ink-demo.cljs:

(ns ink-demo
  (:require ["ink" :refer [render Text]]
            [reagent.core :as r]))

(defonce state (r/atom 0))

(doseq [n (range 1 11)]
  (js/setTimeout #(swap! state inc) (* n 500)))

(defn hello []
  [:> Text {:color "green"} "Hello, world! " @state])

(render (r/as-element [hello]))

Promesa

Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core namespace is included with the let and do! macros. An example:

(ns prom
  (:require [promesa.core :as p]))

(defn sleep [ms]
  (js/Promise.
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
  []
  (p/do!
   (println "Doing stuff which takes a while")
   (sleep 1000)
   1))

(p/let [a (do-stuff)
        b (inc a)
        c (do-stuff)
        d (+ b c)]
  (prn d))
$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while
3

Also see API docs.

Js-interop

Since nbb v0.0.75 applied-science/js-interop is available:

(ns example
  (:require [applied-science.js-interop :as j]))

(def o (j/lit {:a 1 :b 2 :c {:d 1}}))

(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1

Most of this library is supported in nbb, except the following:

  • destructuring using :syms
  • property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.

Examples

See the examples directory for small examples.

Also check out these projects built with nbb:

API

See API documentation.

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.

Build

Prequisites:

  • babashka >= 0.4.0
  • Clojure CLI >= 1.10.3.933
  • Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

  • Clone and cd into this repo
  • bb release

Run bb tasks for more project-related tasks.

Download Details:
Author: borkdude
Download Link: Download The Source Code
Official Website: https://github.com/borkdude/nbb 
License: EPL-1.0

#node #javascript

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 Match Example | Javascript match()

Javascript string match() is an inbuilt function that retrieves the matches when matching a string against a regular expression. Javascript match() method searches the string for the match against the regular expression, and returns the matches, as an Array object.

If a  regular expression does not include the g modifier to perform a global search, then the javascript string match() method will return only the first match in the  string.

Javascript String Match Example

The syntax for the String match() method is the following.

string.match(regexp)

The regexp parameter is required. It is the value to search for, as a regular expression. Let us take an example by creating a file called app.js and add the following code.

We will use the Node.js to run the file and log the output.

// app.js

let str = 'Obama was US president';
let newArray  = str.match(/ba/);
console.log(newArray);

So, in the above example, we have passed the regular expression which is saying that return an array of all the elements satisfying that regular expression.

#javascript #javascript match #regexp #app.js

Lowa Alice

Lowa Alice

1624399200

JavaScript Strings Tutorial

JavaScript Strings

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=09BwruU4kiY&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=6
🔥 If you’re a beginner. I believe the article below will be useful to you ☞ What You Should Know Before Investing in Cryptocurrency - For Beginner
⭐ ⭐ ⭐The project is of interest to the community. Join to Get free ‘GEEK coin’ (GEEKCASH coin)!
☞ **-----CLICK HERE-----**⭐ ⭐ ⭐
Thanks for visiting and watching! Please don’t forget to leave a like, comment and share!

#javascript #strings #javascript strings #javascript strings tutorial

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