Xe Blog

debounce

// 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.
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
var myEfficientFn = debounce(function() {
 // All the taxing stuff you do
}, 250);
window.addEventListener('resize', myEfficientFn);

poll

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

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

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

;(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

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

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]')