Reprinted with 7 Essential JavaScript Functions

Essential JavaScript Functionsby David Walsh Onjune 2, 2015

I Remember the early days of JavaScript where you needed a simple function for just about everything because the browser V  Endors implemented features differently, and not just edge features, basic features, like addEventListener and attachEvent . Times has changed but there is still a few functions each developer should has in their arsenal, for performance for FU Nctional ease purposes.

debounce

The Debounce function can be a game-changer if it comes to event-fueled performance.  If you aren the using a debouncing function with a scroll , resize the key* event, you ' re probably doing it wrong. Here's a debounce function to keep your code efficient:

//Returns a function, that, as long as it continues to be invoked, would not//be triggered. The function would be called after it stops being called for//N milliseconds. If ' immediate ' is passed, trigger the function on the//leading edge, instead of the Trailing.function debounce (func, wait , immediate) {var Timeout;return function () {var context = this, args = Arguments;var later = function () {timeout = Null;i F (!immediate) func.apply (context, args);}; var callnow = immediate &&!timeout;cleartimeout (timeout); timeout = SetTimeout (later, wait); if (Callnow) Func.apply (context, args);};};/ /Usagevar MYEFFICIENTFN = debounce (function () {//All of the taxing stuff do}, Window.addeventlistener (' Resize ', my EFFICIENTFN); 

The function would not allow debounce a callback to being used more than once per given time frame. This was especially important when assigning a callback function to frequently-firing events.

poll

As I mentioned debounce with the function, sometimes you don't get to plug into an event to signify a desired state--if the Event doesn ' t exist, you need-to-check for your desired state at intervals:

function poll (FN, callback, Errback, timeout, interval) {var endTime = number (new Date ()) + (Timeout | |    2000); Interval = Interval | |    100;             (function P () {//If the condition is met, we ' re done!            if (FN ()) {callback ();  }//If the condition isn ' t met but the timeout hasn ' t elapsed, go again else if (number (new Date ())            < EndTime) {setTimeout (P, interval);            }//didn ' t match and too much time, reject!            else {errback (' timed out for ' + fn + ': ' + arguments)); }    })();} Usage:ensure element is Visiblepoll (function () {return document.getElementById (' Lightbox '). offsetwidth &G T    0; }, function () {//Done, Success callback}, function () {//Error, Failure callback}); 

Polling has a long been useful on the web and would continue to being in the future!

once

There is times when you prefer a given functionality only happen once, similar to the the-the-the-the-the-use-an onload event. This code provides said functionality:

Function once (FN, context) {var result;return function () {if (fn) {result = Fn.apply (Context | | this, arguments); fn = nul l;} return result;};} Usagevar canonlyfireonce = once (function () {console.log (' fired! ');}); Canonlyfireonce (); "Fired!" Canonlyfireonce (); Nada

onceThe function ensures a given function can only be called once, thus prevent duplicate initialization!

getAbsoluteUrl

Getting a absolute URL from a variable string is ' t as easy as you think.  There ' s the URL constructor but it can act up if you don't provide the required arguments (which sometimes you can ' t). Here's a suave trick for getting an absolute URLs from and string input:

var Getabsoluteurl = (function () {var a;return function (URL) {if (!a) a = document.createelement (' a '); a.href = Url;return A . href;};}) ();//Usagegetabsoluteurl ('/something '); Http://davidwalsh.name/something

The "Burn" element href handles and URL nonsense for you, providing a reliable absolute URL in return.

isNative

Knowing if a given function is native or not can signal if you ' re willing to override it. This handy code can give you the answer:

;(function () {//used to resolve the internal ' [[Class]] ' of values var toString = Object.prototype.toString;    Used to resolve the decompiled source of functions var fntostring = Function.prototype.toString; Used to detect host constructors (Safari > 4; really typed array specific) var Rehostctor =/^\[object. +?  constructor\]$/;  Compile a regexp using a common native method as a template.  We chose ' object#tostring ' because there ' s a good chance it is not being mucked with.  var renative = RegExp (' ^ ' +//coerce ' object#tostring ' to a string string (toString)//Escape any special REGEXP Characters. Replace (/[.*+?^${} () |[    \]\/\\]/g, ' \\$& ')//Replace mentions of ' toString ' with '. *? ' to keep the template generic.    Replace thing like ' for ... ' to the support environments like Rhino which add extra info//such as method arity. . Replace (/tostring| ( function). *? (? =\\\ () | for. +? (?=\\\]) /g, ' $1.*? ')    + ' $ ');  function Isnative (value) {  var type = typeof value; return type = = ' function '//use ' function#tostring ' to bypass the value ' s own ' toString ' method//and avoid is      ing faked out. ?      Renative.test (Fntostring.call (value))//Fallback to a host object check because some environments would represent      Things like typed arrays as DOM methods which could not conform to the/normal native pattern. : (value && type = = ' object ' && rehostctor.test (Tostring.call (value))) | |  False }//Export however you want module.exports = isnative;} ());//usageisnative (alert); Trueisnative (mycustomfunction); False

The function isn ' t pretty but it gets the job done!

insertRule

We all know so we can grab a NodeList from a selector (via document.querySelectorAll ) and give each of the them a style, but what's more Efficie NT is setting this style to a selector (as you do in a stylesheet):

var sheet = (function () {//Create the <style> tagvar style = document.createelement (' style ');//ADD a media (and/or Media query) Here if you ' d like!//style.setattribute (' media ', ' screen ')//Style.setattribute (' media ', ' only ' screens and ( MAX-WIDTH:1024PX)//WebKit Hack:(style.appendchild (document.createTextNode ("));//Add the <style> element to The pagedocument.head.appendChild (style); return style.sheet;}) ();//Usagesheet.insertrule ("header {float:left; opacity:0.8; } ", 1);

This was especially useful when working on a dynamic, Ajax-heavy site. If you set the "style to a selector", you don't need to account for styling each element, which may match this selector (now O R in the future).

matchesSelector

Oftentimes we validate input before moving forward;  Ensuring a Truthy value, ensuring forms data is valid, etc.  But how often does we ensure an element qualifies for moving forward? You can use a matchesSelector function to validate if an element is a given selector match:

function Matchesselector (el, selector) {var p = element.prototype;var f = p.matches | | p.webkitmatchesselector | | p.mozmat Chesselector | | P.msmatchesselector | | function (s) {return [].indexof.call (Document.queryselectorall (s), this)!==-1;}; Return F.call (el, selector);} Usagematchesselector (document.getElementById (' mydiv '), ' div.someselector[some-attribute=true] ')

There you has it:seven JavaScript functions that every developer should keep in their toolbox.  Have a function I missed? Please share it!

Reprinted with 7 Essential JavaScript Functions