摘要：翻譯正文第一次聲明變量時(shí)，請(qǐng)不要忘記使用關(guān)鍵字聲明使用代替空字符串轉(zhuǎn)成布爾值都為每行代碼的末尾最好都加上個(gè)分號(hào)最好給對(duì)象都添加上構(gòu)造函數(shù)在使用和盡量小心。

翻譯標(biāo)題：45 Useful JavaScript Tips, Tricks and Best Practices

翻譯來(lái)源：http://modernweb.com/2013/12/23/45-useful-javascript-tips-tricks-and-best-practices/

如有翻譯不正確的地方，請(qǐng)?jiān)谙路旁u(píng)論出反饋。

第一次聲明變量時(shí)，請(qǐng)不要忘記使用 var 關(guān)鍵字聲明

使用 === 代替 ==

[10] === 10    // is false
[10]  == 10    // is true
"10" == 10     // is true
"10" === 10    // is false
 []   == 0     // is true
 [] ===  0     // is false
 "" == false   // is true but true == "a" is false
 "" ===   false // is false 

undefined, null, 0, false, NaN, "" (空字符串) 轉(zhuǎn)成布爾值都為false.

每行代碼的末尾最好都加上個(gè)分號(hào)

最好給對(duì)象都添加上構(gòu)造函數(shù)

function Person(firstName, lastName){
    this.firstName =  firstName;
    this.lastName = lastName;        
}  

var Saad = new Person("Saad", "Mousliki");

在使用typeof,instanceof和constructor盡量小心。

善用匿名自調(diào)用函數(shù)(IIFE)

(function(){
    // some private code that will be executed automatically
})();  
(function(a,b){
    var result = a+b;
    return result;
})(10,20)

在一個(gè)數(shù)組中獲取一個(gè)隨機(jī)的項(xiàng)目

var items = [12, 548 , "a" , 2 , 5478 , "foo" , 8852, , "Doe" , 2145 , 119];
var  randomItem = items[Math.floor(Math.random() * items.length)];

在指定范圍內(nèi)獲取一個(gè)隨機(jī)數(shù)

var x = Math.floor(Math.random() * (max - min + 1)) + min;

生成一個(gè)0到指定最大值的數(shù)字?jǐn)?shù)組。

var numbersArray = [] , max = 100;

for( var i=1; numbersArray.push(i++) < max;);  // numbers = [1,2,3 ... 100] 

隨機(jī)生成指定長(zhǎng)度的字符串

function generateRandomAlphaNum(len) {
    var rdmString = "";
    for( ; rdmString.length < len; rdmString  += Math.random().toString(36).substr(2));
    return  rdmString.substr(0, len);

}

對(duì)一個(gè)數(shù)字?jǐn)?shù)組隨機(jī)排序

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];
numbers = numbers.sort(function(){ return Math.random() - 0.5});

去掉字符串的前后空格

String.prototype.trim = function(){return this.replace(/^s+|s+$/g, "");};  

將一個(gè)數(shù)組添加到另一個(gè)數(shù)組

var array1 = [12 , "foo" , {name "Joe"} , -2458];

var array2 = ["Doe" , 555 , 100];
Array.prototype.push.apply(array1, array2);

將arguments轉(zhuǎn)換成數(shù)組

var argArray = Array.prototype.slice.call(arguments);

驗(yàn)證給定參數(shù)是否為數(shù)字

function isNumber(n){
    return !isNaN(parseFloat(n)) && isFinite(n);
}

驗(yàn)證給定的參數(shù)是否為數(shù)組

function isArray(obj){
    return Object.prototype.toString.call(obj) === "[object Array]" ;
}

獲取數(shù)字?jǐn)?shù)組中的最大值和最小值

var  numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411]; 
var maxInNumbers = Math.max.apply(Math, numbers); 
var minInNumbers = Math.min.apply(Math, numbers);

清空一個(gè)數(shù)組

var myArray = [12 , 222 , 1000 ];  
myArray.length = 0; // myArray will be equal to [].

不要使用delete來(lái)刪除數(shù)組中的項(xiàng)目

請(qǐng)使用splice來(lái)代替deletel來(lái)刪除數(shù)組中的項(xiàng)目，使用delete會(huì)用undefinedl來(lái)替換數(shù)組中被刪除的哪一項(xiàng)。

delete

var items = [12, 548 ,"a" , 2 , 5478 , "foo" , 8852, , "Doe" ,2154 , 119 ]; 
items.length; // return 11 
delete items[3]; // return true 
items.length; // return 11 
/* items will be equal to [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154,       119]   */

splice

var items = [12, 548 ,"a" , 2 , 5478 , "foo" , 8852, , "Doe" ,2154 , 119 ]; 
items.length; // return 11 
items.splice(3,1) ; 
items.length; // return 10 
/* items will be equal to [12, 548, "a", 5478, "foo", 8852, undefined × 1, "Doe", 2154,       119]   */

用長(zhǎng)度來(lái)截取一個(gè)字符串

var myArray = [12 , 222 , 1000 , 124 , 98 , 10 ];  
myArray.length = 4; // myArray will be equal to [12 , 222 , 1000 , 124].

在條件判斷里面使用邏輯AND或者OR

var foo = 10;  
foo == 10 && doSomething(); // 等效 if (foo == 10) doSomething(); 
foo == 5 || doSomething(); // 等效 if (foo != 5) doSomething();

默認(rèn)值取值

function doSomething(arg1){ 
    arg1 = arg1 || 10; // 如果arg1沒(méi)有被賦值，則取10
}

使用map()函數(shù)來(lái)遍歷數(shù)組

var squares = [1,2,3,4].map(function (val) {  
    return val * val;  
}); 
// squares will be equal to [1, 4, 9, 16]       

獲取指定精度的數(shù)字

var num =2.443242342;
num = num.toFixed(4);  // num will be equal to 2.4432

浮點(diǎn)數(shù)小數(shù)點(diǎn)的問(wèn)題

0.1 + 0.2 === 0.3 // is false 
9007199254740992 + 1 // is equal to 9007199254740992  
9007199254740992 + 2 // is equal to 9007199254740994

你可以使用toFixed()或者toPrecision()來(lái)解決這類問(wèn)題

當(dāng)使用for-in來(lái)迭代一個(gè)對(duì)象時(shí)，檢查其屬性

for (var name in object) {  
    if (object.hasOwnProperty(name)) { 
        // do something with name                    
    }  
}

這段代碼可以用來(lái)避免迭代自己內(nèi)部的屬性

逗號(hào)運(yùn)算符

var a = 0; 
var b = ( a++, 99 ); 
console.log(a);  // a will be equal to 1 
console.log(b);  // b is equal to 99

當(dāng)一個(gè)變量需要被查詢或者計(jì)算的時(shí)候，可以把它緩存起來(lái)

var navright = document.querySelector("#right"); 
var navleft = document.querySelector("#left"); 
var navup = document.querySelector("#up"); 
var navdown = document.querySelector("#down");

使用isFinite()來(lái)驗(yàn)證一個(gè)參數(shù)在傳遞之前

isFinite(0/0) ; // false 
isFinite("foo"); // false 
isFinite("10"); // true 
isFinite(10);   // true 
isFinite(undefined);  // false 
isFinite();   // false 
isFinite(null);  // true  !!! 

避免在數(shù)組中使用負(fù)值索引

var numbersArray = [1,2,3,4,5]; 
var from = numbersArray.indexOf("foo") ;  // from is equal to -1 
numbersArray.splice(from,2);    // will return [5]

序列和解析一個(gè)JSON

var person = {name :"Saad", age : 26, department : {ID : 15, name : "R&D"} }; 
var stringFromPerson = JSON.stringify(person); 
/* stringFromPerson is equal to "{"name":"Saad","age":26,"department":{"ID":15,"name":"R&D"}}"   */ 
var personFromString = JSON.parse(stringFromPerson);  
/* personFromString is equal to person object  */

避免使用 eval() 桌和 Function 構(gòu)造函數(shù)

var func1 = new Function(functionCode);
var func2 = eval(functionCode);

避免使用使用 with()

避免使用 for-in 來(lái)迭代一個(gè)數(shù)組

對(duì)于setTimeout() 和 setInterval(),最好傳遞函數(shù)而不是字符串。

使用switch/case來(lái)替代多重if/else

把switch/case用在數(shù)據(jù)分類上

function getCategory(age) {  
    var category = "";  
    switch (true) {  
        case isNaN(age):  
            category = "not an age";  
            break;  
        case (age >= 50):  
            category = "Old";  
            break;  
        case (age <= 20):  
            category = "Baby";  
            break;  
        default:  
            category = "Young";  
            break;  
    };  
    return category;  
}  
getCategory(5);  // will return "Baby"

創(chuàng)建一個(gè)對(duì)象，并且他的原型是我們指定的對(duì)象。

function clone(object) {  
    function OneShotConstructor(){}; 
    OneShotConstructor.prototype= object;  
    return new OneShotConstructor(); 
} 
clone(Array).prototype ;  // []

一個(gè) HTML 實(shí)體替換函數(shù)

function escapeHTML(text) {  
    var replacements= {"<": "<", ">": ">","&": "&", """: """};                      
    return text.replace(/[<>&"]/g, function(character) {  
        return replacements[character];  
    }); 
}

避免在循環(huán)中使用 try-catch-finally

不好的用法：

for (i = 0, len = object.length; i 

好的用法：

var object = ["foo", "bar"], i;  
try { 
    for (i = 0, len = object.length; i 


對(duì)XMLHttpRequests設(shè)置定時(shí)失效的時(shí)間

var xhr = new XMLHttpRequest (); 
xhr.onreadystatechange = function () {  
    if (this.readyState == 4) {  
        clearTimeout(timeout);  
        // do something with response data 
    }  
}  
var timeout = setTimeout( function () {  
    xhr.abort(); // call error callback  
}, 60*1000 /* timeout after a minute */ ); 
xhr.open("GET", url, true);  

xhr.send();



解決 WebSocket的失效時(shí)間

var timerID = 0; 
function keepAlive() { 
    var timeout = 15000;  
    if (webSocket.readyState == webSocket.OPEN) {  
        webSocket.send("");  
    }  
    timerId = setTimeout(keepAlive, timeout);  
}  
function cancelKeepAlive() {  
    if (timerId) {  
        cancelTimeout(timerId);  
    }  
}



記住使用原生的運(yùn)算符代替函數(shù)調(diào)用。使用VanillaJS.

示例demo

var min = Math.min(a,b); 
A.push(v);

使用下面代替上面的demo

var min = a < b ? a : b; 
A[A.length] = v;


不要忘記在編碼的時(shí)候規(guī)范美化。在部署的時(shí)候用JSLIint和壓縮


JavaScript 是令人敬畏。學(xué)習(xí)JavaScript最好的資源