angular debounce throttle

throttle

我们这里说的throttle就是函数节流的意思。再说的通俗一点就是函数调用的频度控制器，是连续执行时间间隔控制。主要应用的场景比如：

• 鼠标移动，mousemove 事件
• DOM 元素动态定位，window对象的resize和scroll 事件

有人形象的把上面说的事件形象的比喻成机关枪的扫射，throttle就是机关枪的扳机，你不放扳机，它就一直扫射。我们开发时用的上面这些事件也是一样，你不松开鼠标，它的事件就一直触发。回到window resize和scroll事件的基本优化提到的优化：

var resizeTimer=null;
$(window).on('resize',function(){
       if(resizeTimer){
           clearTimeout(resizeTimer)
       }
       resizeTimer=setTimeout(function(){
           console.log("window resize");
       },400);
   }
);

setTimeout和clearTimeout其实就是一个简单的 throttle，很多好的控制了resize事件的调用频度。

debounce

debounce和throttle很像，debounce是空闲时间必须大于或等于 一定值的时候，才会执行调用方法。debounce是空闲时间的间隔控制。比如我们做autocomplete，这时需要我们很好的控制输入文字时调用方法时间间隔。一般时第一个输入的字符马上开始调用，根据一定的时间间隔重复调用执行的方法。对于变态的输入，比如按住某一个建不放的时候特别有用。

debounce主要应用的场景比如：

• 文本输入keydown 事件，keyup 事件，例如做autocomplete

这类网上的方法有很多，比如Underscore.js就对throttle和debounce进行封装

angular 1.3版本之后可以使用 ngModelOptions参数在设置相应的debounce

ngModelOptionsObject

options to apply to the current model. Valid keys are:

• updateOn: string specifying which event should the input be bound to. You can set several events using an space delimited list. There is a special event called default that matches the default events belonging of the control.
• debounce: integer value which contains the debounce model update value in milliseconds. A value of 0 triggers an immediate update. If an object is supplied instead, you can specify a custom value for each event. For example:ng-model-options="{ updateOn: 'default blur', debounce: { 'default': 500, 'blur': 0 } }"
• allowInvalid: boolean value which indicates that the model can be set with values that did not validate correctly instead of the default behavior of setting the model to undefined.
• getterSetter: boolean value which determines whether or not to treat functions bound tongModel as getters/setters.
• timezone: Defines the timezone to be used to read/write the Date instance in the model for<input type="date">, <input type="time">, ... . It understands UTC/GMT and the continental US time zone abbreviations, but for general use, use a time zone offset, for example, '+0430' (4 hours, 30 minutes east of the Greenwich meridian) If not specified, the timezone of the browser will be used.

1.2版本之前的可以自行进行封装：

angular.module('lz.utils.debounce', [])        .service('$debounce', ['$timeout', function ($timeout) {            return function (func, wait, immediate, invokeApply) {                var timeout, args, me, result;                function debounce() {                    /* jshint validthis:true */                    me = this;                    args = arguments;                    var later = function () {                        timeout = null;                        if (!immediate) {                            result = func.apply(me, args);                        }                    };                    var callNow = immediate && !timeout;                    if (timeout) {                        $timeout.cancel(timeout);                    }                    timeout = $timeout(later, wait, invokeApply);                    if (callNow) {                        result = func.apply(me, args);                    }                    return result;                }                debounce.cancel = function () {                    $timeout.cancel(timeout);                    timeout = null;                };                return debounce;            };        }])    /**     * usage: <XX lz-debounce="500" immediate="true" ng-model="test"></XX>     */        .directive('lzDebounce', ['$debounce', '$parse', function (debounce, $parse) {            return {                require: 'ngModel',                priority: 999,                link: function ($scope, $element, $attrs, ngModelController) {                    var debounceDuration = $parse($attrs.debounce)($scope);                    var immediate = !!$parse($attrs.immediate)($scope);                    var debouncedValue, pass;                    var prevRender = ngModelController.$render.bind(ngModelController);                    var commitSoon = debounce(function (viewValue) {                        pass = true;                        ngModelController.$$lastCommittedViewValue = debouncedValue;                        ngModelController.$setViewValue(viewValue);                        pass = false;                    }, parseInt(debounceDuration, 10), immediate);                    ngModelController.$render = function () {                        prevRender();                        commitSoon.cancel();                        //we must be first parser for this to work properly,                        //so we have priority 999 so that we unshift into parsers last                        debouncedValue = this.$viewValue;                    };                    ngModelController.$parsers.unshift(function (value) {                        if (pass) {                            debouncedValue = value;                            return value;                        } else {                            commitSoon(ngModelController.$viewValue);                            return debouncedValue;                        }                    });                }            };        }]);