Seven JavaScript functions that every developer should keep in their toolbox.
// ----------------------------------------------------------------------------
// 7 Essential JavaScript Functions
//
// Seven JavaScript functions that every developer should keep in their toolbox.
//
// I remember the early days of JavaScript where you needed a simple function
// for just about everything because the browser vendors implemented features
// differently, and not just edge features, basic features, like
// addEventListener and attachEvent. Times have changed but there are still a
// few functions each developer should have in their arsenal, for performance
// for functional ease purposes.
//
// http://davidwalsh.name/essential-javascript-functions
// ----------------------------------------------------------------------------
// debounce (1)
//
// Returns a function, that, as long as it continues to be invoked, will not be
// triggered. The function will 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.
//
// The debounce function will not allow a callback to be used more than once per
// given time frame. This is especially important when assigning a callback
// function to frequently-firing events.
function debounce(func, wait, immediate) {
var timeout;
return function () {
var context = this,
args = arguments;
var later = function () {
timeout = null;
if (!immediate) {
func.apply(context, args);
}
};
var callNow = immediate && !timeout;
clearTimeout(timeout);
timeout = setTimeout(later, wait);
if (callNow) {
func.apply(context, args);
}
};
}
//
// Usage
//
// You'll pass the debounce function the function to execute and the fire rate
// limit in milliseconds. Here's an example usage:
var myEfficientFn = debounce(function() {
// All the taxing stuff you do...
console.log('myEfficientFn.resize', 'debounce');
}, 250);
window.addEventListener('resize', myEfficientFn);
/**
* debounce (2)
*
* The debounce function is an extremely useful tool that can help throttle
* requests. It is different to throttle though as throttle will allow only one
* request per time period, debounce will not fire immediately and wait the
* specified time period before firing the request. If there is another request
* made before the end of the time period then we restart the count. This can be
* extremely useful for calling functions that often get called and are only
* needed to run once after all the changes have been made.
*
* http://modernjavascript.blogspot.co.uk/2013/08/building-better-debounce.html
*
* @param {Function} func
* @param {Number} wait
*/
var debounce = function (func, wait) {
// we need to save these in the closure
var timeout, args, context, timestamp;
return function () {
// save details of latest call
context = this;
args = [].slice.call(arguments, 0);
timestamp = new Date();
// this is where the magic happens
var later = function () {
// how long ago was the last call
var last = (new Date()) - timestamp;
// if the latest call was less that the wait period ago
// then we reset the timeout to wait for the difference
if (last < wait) {
timeout = setTimeout(later, wait - last);
// or if not we can null out the timer and run the latest
} else {
timeout = null;
func.apply(context, args);
}
};
// we only need to set the timer now if one isn't already running
if (!timeout) {
timeout = setTimeout(later, wait);
}
};
};
/**
* debounce (3)
*
* Hello! Thanks for your nice and clean debounce function. Lodash's is powerful
* but overly complicated for most use. I optimized your code and also wrote it
* for ES6.
*
* 1. You only need timeout to be outside the returned closure. The rest of the vars can go inside.
* 2. You can use Date.now() instead of new Date().
* 3. You don't need to save the context for the func.apply(), you can just pass null.
* 4. You can use a ternary to return an IIFE which returns nothing to set the timeout variable to undefined.
*
* https://github.com/rhysbrettbowen/debounce/issues/2
*
* @param {Number} wait
* @param {Function} func
*/
var debounce = function(wait, func) {
var timeout;
return function() {
var last,
args = [].slice.call(arguments, 0),
timestamp = Date.now(),
later = function() {
(last = Date.now() - timestamp),
(timeout =
wait > last
? setTimeout(later, wait - last)
: (function() {
func.apply(null, args);
})());
};
timeout || (timeout = setTimeout(later, wait));
};
};
// poll
//
// As I mentioned with the debounce 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(new Error('timed out for ' + fn + ': ' + arguments));
}
})();
}
// Usage: ensure element is visible
poll(
function () {
return document.getElementById('lightbox').offsetWidth > 0;
},
function () {
// Done, success callback
},
function () {
// Error, failure callback
}
);
// once
//
// There are times when you prefer a given functionality only happen once,
// similar to the way you'd use an onload event. This code provides you said
// functionality:
//
// The once function ensures a given function can only be called once, thus
// prevent duplicate initialization!
//
// Also see:
// https://jonlabelle.com/snippets/view/javascript/limit-function-calls-to-once
function once(fn, context) {
var result;
return function () {
if (fn) {
result = fn.apply(context || this, arguments);
fn = null;
}
return result;
};
}
// Usage
var canOnlyFireOnce = once(function () {
console.log('Fired!');
});
canOnlyFireOnce(); // "Fired!"
canOnlyFireOnce(); // nada
// getAbsoluteUrl
//
// Getting an absolute URL from a variable string isn'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 URL from and string input:
//
// The "burn" element href handles and URL nonsense for you, providing a
// reliable absolute URL in return.
var getAbsoluteUrl = (function () {
var a;
return function (url) {
if (!a) {
a = document.createElement('a');
}
a.href = url;
return a.href;
};
})();
// Usage
getAbsoluteUrl('/something'); // http://davidwalsh.name/something
// 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:
//
// The function isn't pretty but it gets the job done!
(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 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 being faked out.
? reNative.test(fnToString.call(value))
// Fallback to a host object check because some environments will represent
// things like typed arrays as DOM methods which may not conform to the
// normal native pattern.
: (value && type == 'object' && reHostCtor.test(toString.call(value))) || false;
}
// export however you want
module.exports = isNative;
}());
// Usage
isNative(alert); // true
isNative(myCustomFunction); // false
// insertRule
//
// We all know that we can grab a NodeList from a selector (via
// document.querySelectorAll) and give each of them a style, but what's more
// efficient is setting that style to a selector (like you do in a stylesheet):
//
// This is 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 that may match that selector (now or in the future).
var sheet = (function () {
// Create the <style> tag
var style = document.createElement('style');
// Add a media (and/or media query) here if you'd like!
// style.setAttribute('media', 'screen')
// style.setAttribute('media', 'only screen and (max-width : 1024px)')
// WebKit hack :(
style.appendChild(document.createTextNode(''));
// Add the <style> element to the page
document.head.appendChild(style);
return style.sheet;
})();
// Usage
sheet.insertRule("header { float: left; opacity: 0.8; }", 1);
// matchesSelector
//
// Oftentimes we validate input before moving forward; ensuring a truthy value,
// ensuring forms data is valid, etc. But how often do we ensure an element
// qualifies for moving forward? You can use a matchesSelector function to
// validate if an element is of a given selector match:
function matchesSelector(el, selector) {
var p = Element.prototype;
var f = p.matches || p.webkitMatchesSelector || p.mozMatchesSelector || p.msMatchesSelector || function (s) {
return [].indexOf.call(document.querySelectorAll(s), this) !== -1;
};
return f.call(el, selector);
}
// Usage
matchesSelector(document.getElementById('myDiv'), 'div.someSelector[some-attribute=true]')