變量var的使用

js的變量沒有類型

var $li = $('#' + file.id),$percent = $li.find('.progress span');//console.log("percentage:", percentage);// 避免重復創建if (!$percent.length) {$percent = $('<p class="progress"><span></span></p>').appendTo($li).find('span');}

如果是null不會進入if

如果是一個數組會進入

空字符串不會進入

如果是undefined不會進入

如果是1會進入

如果是0不會進入

如果是字符串1也會進入

ES6 改變了現狀， 引入了新的 let 關鍵字， 提供了除 var 以外的另一種變量聲明方式。

let 關鍵字可以將變量綁定到所在的任意作用域中（通常是 { .. } 內部）。 換句話說， let為其聲明的變量隱式地了所在的塊作用域。

與var不同的是，它聲明的變量只能是全局或者整個函數塊的。換句話，塊級 == { }

let 聲明的變量只是在其聲明的塊或者子塊中可用，這一點，與var相似。二者的主要區別在于var聲明的變量的作用域是整個封閉函數，而let聲明的作用域是塊。

1 function varTest() {2 var x = 1;3 if (true) {4 var x = 2; // 同樣的變量!5 console.log(x); // 26 }7 console.log(x); // 28 }9 10 function letTest() { 11 let x = 1; 12 if (true) { 13 let x = 2; // 不同的變量 14 console.log(x); // 2 15 } 16 console.log(x); // 1 17 }

當用到內部函數時候，let 會讓你的代碼更加簡潔。

1 var list = document.getElementById('list');2 3 for (let i = 1; i <= 5; i++) {4 let item = document.createElement('li');5 item.appendChild(document.createTextNode('Item ' + i));6 7 item.onclick = function(ev) {8 console.log('Item ' + i + ' is clicked.');9 }; 10 list.appendChild(item); 11 } 12 13 // to achieve the same effect with 'var' 14 // you have to create a different context 15 // using a closure to preserve the value 16 for (var i = 1; i <= 5; i++) { 17 var item = document.createElement('li'); 18 item.appendChild(document.createTextNode('Item ' + i)); 19 20 (function(i){ 21 item.onclick = function(ev) { 22 console.log('Item ' + i + ' is clicked.'); 23 }; 24 })(i); 25 list.appendChild(item); 26 }

以上示例的工作原理是因為（匿名）內部函數的五個實例引用了變量i的五個不同實例。注意，如果將let 替換為 var， 則它將無法正常工作，因為所有內部函數都將返回相同的i，6是最終值。此外我們可以通過將創建新元素的代碼移動到每個循環的作用域來保持循環更清晰。

在程序或者函數的頂層，let 并不會像var 一樣在全局對象上創建一個屬性，比如：

1 var x = "apple"; 2 let y = "apple"; 3 console.log(this.x); //'apple' 4 console.log(this.y); //undefined

在處理構造函數的時候，可以通過let 綁定來共享一個或者多個私有成員，而不使用閉包：

1 var Thing;2 {3 let privateScope = new WeakMap();4 let counter = 0;5 6 Thing = function(){7 this.someProperty = 'foo';8 privateScope.set(this, {9 hidden: ++counter, 10 }); 11 }; 12 13 Thing.prototype.showPublic = function(){ 14 return this.someProperty; 15 }; 16 17 Thing.prototype.showPrivate = function(){ 18 return privateScope.get(this).hidden; 19 }; 20 } 21 22 console.log(typeof privateScope); //undefined 23 24 var thing = new Thing(); 25 console.log(thing); //Thing { someProperty: 'foo' } 26 console.log(thing.showPublic()); //foo 27 console.log(thing.showPrivate()); //1

當在塊中使用時，let 將變量的作用域限制為該塊。注意var 的作用域在它被聲明的函數內區別。

1 var a = 1;2 var b = 2;3 4 if(a === 1){5 var a = 11;6 let b = 22;7 8 console.log(a); // 119 console.log(b); // 22 10 } 11 console.log(a); // 11 12 console.log(b); // 2

總之，let 的作用域是自己最近的{}

var names = ["00:00","23:00","22:00","21:00","20:00","19:00","18:00","17:00","16:00","15:00","14:00","13:00","12:00","11:00","10:00","09:00","08:00","07:00","06:00","05:00","04:00","03:00","02:00","01:00"];var url = CONTEXT_PATH +"/cusviews/dev/getRadarChartName";var param = {deviceCode:deviceCode}var retData = $.getData(url,param)if(1000!=retData.status){return;}var data = retData.data;if(null==data){return;}var rlt = {"data" : []};var rltdata = [];var dataList = new Array();function isInArray(arr,value){for(var i = 0; i < arr.length; i++){if(value === arr[i]){return true;}}return false;}$.each(data.textlist,function(j,k){let obj = {};if(isInArray(names,k.substring(11,16))){obj.text = k.substring(11,13);}else{obj.text = "";}obj.max = data.maxlist[j];rlt.data.push(obj);}) window.onload = function() {var sum = 0;for (var i = 0;i <10;i++){sum += i; }alert(sum);alert("i="+i); } </script> --------------------- 上面的代碼可輸出i <script> window.onload = function() {var sum = 0;for (let i = 0;i <10;i++){sum += i; }alert(sum);alert("i="+i); } </script> --------------------- i未定義

let具有自己的塊級作用域，所以for循環轉一次，創建一個塊級作用域，思路與閉包相同，分別儲存了5個不同的i變量。

var lis = document.getElementsByTagName("li"); for(let i=0; i<lis.length;i++){ lis[i].onclick = function(){ alert(i); } } (function () {})();(function ($) {}) (jQuery) (function (window, $) {})(window, jQuery);(function (window, $, undefined) {})(window, jQuery);

var _util = function () {this.QueryFormSerializeArray = function (domid) {var form = null;if (typeof (domid) === "string")from = $('#' + domid);elsefrom = domid;var p = from.serializeArray();var s = $.map(p, function (n) {var t = $("#" + n.name);if (t.size() == 0)t = from.find("*[textboxname='" + n.name + "']");var query = {};var s = $.trim(t.attr('data-query'));if (s) {if (s.substring(0, 1) != '{') {s = '{' + s + '}';}query = (new Function('return ' + s))();if (query.filed) {query.name = query.filed;//query.remove("filed");}}//console.log(query);return $.extend({}, n, query);});return s;};/*** 序列化Form 返回字符串* @param {string} domid* @return {any} 序列化后的*/this.QueryFormSerializeString = function (domid) {var s = this.QueryFormSerializeArray(domid);var strpars = JSON.stringify(s);return strpars;}; };$Core.util = new _util();

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function ($)，直接進入

$.extend({renderSelectorMyf : function(options){return new renderSelectorMy(options);}});

new實例化的時候進入方法

;(function($){ debugger;var options = {fieldCode: "gfyId",url: "../../Security/selector/user/PublicServiceUserList.html?s=" + Math.random(),multi: false,code: "gfyId,gfyIdName",keyRespField: "gfyId,id",dictCode: "publicserviceName",area: ['90%','90%']};/*引用查詢選擇*/function renderSelectorMy(options){var defaults = {};this.settings = $.extend({},defaults,options);var $domObj = $("#" + this.settings.fieldCode + "-popSelector");this.settings.url = $domObj.attr("action") ? $domObj.attr("action") : this.settings.url;this.settings.multi = $domObj.attr("multi") ? $domObj.attr("multi") : this.settings.multi;this.settings.code = $domObj.attr("codeAndName") ? $domObj.attr("codeAndName").split(",") : this.settings.code.split(",");this.settings.keyRespField = this.settings.keyRespField ? this.settings.keyRespField.split(",") : "";this.init();}//為函數添加原型鏈上的方法renderSelectorMy.prototype = {init: function(){var _self = this,_keys = _self.settings.code;$("input[name='" + _keys[0] +"']").parent().parent().find("button").unbind('click').bind('click', function(){var action = "_self." + $(this).attr("action");eval(action);});},querySelect : function(thi,event){var _self = this;var url = _self.settings.url;var _keys = _self.settings.code;var keyRespField = _self.settings.keyRespField;var id = keyRespField[1];var ids = $("input[name='" + _keys[0] +"']").val();if(url.indexOf("?") != -1) {url = url + "&" + id + "="+ids;}else {url = url + "?" + id + "="+ids;}$Core.UI.openDialog("selwind", url,{title: "列表選擇",width: _self.settings.area[0],height: _self.settings.area[1],onClose: function () {}});},echoSelect : function(_data){var _self = this;var data = _data.data,_keys = _self.settings.code,_rkeys = _self.settings.keyRespField,dictName = "",dictCode = _self.settings.dictCode;$Core.DicCache.initDictionary(dictCode,function(dicts){var _dicts = dicts;if(dicts && dicts.data){var dictDatas = dicts.data[dictCode];for(var i=0,len=dictDatas.length; i<len; i++){var item = dictDatas[i];if(data[_keys[0]] == item[_rkeys[1]]){var itemName = item.text;dictName += itemName +",";}}$("span input:text", $("div #" + _keys[0] + "-popSelector")).val(dictName.substr(0,dictName.length-1));}else{$("span input:text", $("div #" + _keys[0] + "-popSelector")).val(dictName);}})},selectResultAfterCallback: function(checkRlt){var _self = this,multi = _self.settings.multi;if(checkRlt.length == 0){$Core.UI.message.warning("選請選擇數據!");}if(!multi && checkRlt.length != 1){$Core.UI.message.warning("單選,請選擇一條數據!");}var _keys = _self.settings.code,code = "",name = "";if(!_self.settings.multi){code = checkRlt[0]['code'];name = checkRlt[0]['name'];}else{var _code = "",_name = "";for(var i=0,len=dataArr.length; i<len; i++){_code += checkRlt[i]['code'] +",";_name += checkRlt[i]['name'] +",";}code = _code.substring(0,_code.length-1);name = _name.substring(0,_name.length-1);}//給input[name='']:text 賦值address = checkRlt[0]['address'];headPerson = checkRlt[0]['headPerson'];headPersonPhone = checkRlt[0]['headPersonPhone'];customerType = checkRlt[0]['customerType'];$("input[name='address']").val(address);$("input[name='headPerson']").val(headPerson);$("input[name='headPersonPhone']").val(headPersonPhone);/*$("input[name='customerType']").val(customerType);*/$("#customerType").combobox("setValue", customerType);$("input[name='" + _keys[0] + "']:hidden").val(code);$("span input:text", $("div #" + _keys[0] + "-popSelector")).val(name);$(".panel-tool-close").trigger('click');}} //擴展jquery類方法$.extend({renderSelectorMyf : function(options){return new renderSelectorMy(options);}}); })(jQuery) debugger; renderSelector = $.renderSelectorMyf({fieldCode: "gfyId",url: "../../Security/selector/user/PublicServiceUserList.html?s=" + Math.random(),multi: false,code: "gfyId,gfyIdName",keyRespField: "gfyId,id",dictCode: "publicserviceName",area: ['90%','90%']});_self.renderSelectors = [renderSelector];

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