Web程序员必备的7个JavaScript函数

// 返回一个函数，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); };};// Usagevar myEfficientFn = debounce(function() { // All the taxing stuff you do}, 250);window.addEventListener('resize', myEfficientFn);

function poll (fn, callback, err, timeout, interval) { var startTime = (new Date()).getTime(); var pi = window.setInterval(function(){  if (Math.floor(((new Date).getTime() - startTime) / 1000) <= timeout) {   if (fn()) {    callback();   }  } else {   window.clearInterval(pi);   err();  } }, interval)}

function once(fn, context) {  var result; return function() {  if(fn) { result = fn.apply(context || this, arguments); fn = null; } return result; };}// Usagevar canOnlyFireOnce = once(function() { console.log('Fired!');});canOnlyFireOnce(); // "Fired!"canOnlyFireOnce(); // nada

var getAbsoluteUrl = (function() { var a; return function(url) { if(!a) a = document.createElement('a'); a.href = url; return a.href; };})();// UsagegetAbsoluteUrl('/something'); 

;(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;}());// UsageisNative(alert); // trueisNative(myCustomFunction); // false

// Build a better Sheet object Sheet = (function() { // Build style var style = document.createElement('style'); style.setAttribute('media', 'screen'); style.appendChild(document.createTextNode('')); document.head.appendChild(style); // Build and return a single function return function(rule){ style.sheet.insertRule( rule, style.sheet.cssRules.length ); } ;})();// Then call as a functionSheet(".stats { position: relative ; top: 0px }") ;

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);}// UsagematchesSelector(document.getElementById('myDiv'), 'div.someSelector[some-attribute=true]')