经常在各处牛人的代码中看到许多简写的条件表达语句,看了一些介绍这方面的文章,觉得3 ways 2 say if这篇文章(http://www.thomasfrank.se/3_ways_2_say_if.html)还不错。在这篇文章中作者对传统的if...else...、"color: #ff0000">1. if...else结构

// Set r to 0 or 1 
var r= Math.floor(2*Math.random()) 
 
// Set a, b and c to "small" if r==0 an else set them to "big" 
// using three different techniques 
 
// Method 1: If else 
var a; if (r==0){a = "small"} else {a = "big"}; 
 
// Method 2: Conditional operator 
var b = r==0 "small" : "big"; 
 
// Method 3: And/or operators 
var c = r==0 && "small" || "big"; 
 
// Check the values of our variables 
alert(r+" "+a+" "+b+" "+c);

2. if...else if...else结构

// Set r to 0,1,2 or 3 
var r= Math.floor(4*Math.random()) 
 
// Set a, b and c to "nada","small","big" and "huge" 
// depending on the value or r using three different techniques 
 
// Method 1: If.. else if... else 
var a; 
if (r==0){a="nada"} 
else if (r==1){a="small"} 
else if (r==2){a="big"} 
else {a="huge"}; 
 
// Method 2: Conditional operators 
var b = 
r==0 "nada" 
: r==1 "small" 
: r==2 "big" 
: "huge"; 
 
// Method 3: And/or operators 
var c = 
r==0 && "nada" 
|| r==1 && "small" 
|| r==2 && "big" 
|| "huge"; 
 
// Check the values of our variables 
alert(r+" "+a+" "+b+" "+c);

3. 执行函数

// Set r to 0,1,2 or 3 
var r= Math.floor(4*Math.random()) 
 
// The global variable x and our four functions 
var x=""; 
nada=function(){x+="Nada! "}; 
small=function(){x+="Small! "}; 
big=function(){x+="Big! "}; 
huge=function(){x+="Huge! "}; 
 
// Call a specific function depending on the value of r 
// using three different techniques 
 
// Method 1: If.. else if... else 
if (r==0){nada()} 
else if (r==1){small()} 
else if (r==2){big()} 
else {huge()}; 
 
// Method 2: Conditional operators 
r==0 " "+x);

4. 执行代码

// Set r to 0,1,2 or 3 
var r= Math.floor(4*Math.random()) 
 
// The global variable x 
var x=""; 
 
// Executing different code depending on the value of r 
// using three different techniques 
 
// Method 1: If.. else if... else 
if (r==0){x+="Nada! "} 
else if (r==1){x+="Small! "} 
else if (r==2){x+="Big! "} 
else {x+="Huge! "}; 
 
// Method 2: Conditional operators 
r==0 "Nada! "}() 
: r==1 "Small! "}() 
: r==2 "Big! "}() 
: function(){x+="Huge! "}(); 
 
// Method 3: And/or operators 
r==0 && (function(){x+="Nada! "}() || true) 
//有人在评论中指出这里的匿名函数是不必需的,在只有一条可执行代码时是这样的,但是如果有多条代码需要执行,匿名函数还是不错的
|| r==1 && (function(){x+="Small! "}() || true) 
|| r==2 && (function(){x+="Big! "}() || true) 
|| function(){x+="Huge! "}(); 
 
// Check the values of our variables 
alert(r+" "+x);

在这篇网文中,作者的关注重心是代码的简短与否,所以在一般情况下实现同等功能,作者更倾向于使用"color: #000080">其一、当用逻辑与&&和逻辑或||运算符运算时,方向都是自左向右的,&&运算到第一个值为false的条件(或可转换为false的值,如null/undefined/0/""/NaN等)时停止,而运算到第一个值为true的条件(或可转换为true的值)时停止;整个条件返回的值是最后检测的条件的值,不一定只是true/false。

其二、逻辑与&&运算符较逻辑或运算符相比,前者有更高的优先级。

根据第一个原则,r==0和"small"按自左向右的顺序计算,如果r==0为true,则检测"small","small"为非空字符串,故这样c取值为"small";如果r==0为false,则直接开始逻辑或||的第二个条件"big"检测,同样的道理,c应当取值为"big"。根据第二个原则,在对上述代码中的变量c的运算过程中,没有必要加括号。

由于使用"htmlcode">

var myObj = function(options) {
  var color = options.color || this.defaults.defaults;
  var backgroundColor = options.backgroundColor
      || this.defaults.backgroundColor;
};
myObj.prototype.defaults = {
  color : "#393939",
  backgroundColor : "#222"
}
var myIns = new myObj({
  color : "#80FF80"
});
console.log("color:"+myIns.color+", backgroundColor: "+myIns.backgroundColor);

不管用"htmlcode">

(xmlHttpRequest.readyState==4 && xmlHttpRequest.status ==200) "Success!"): alert("Failure!");

所以如果有多条代码需要执行,就应该用匿名函数。如:

(xmlHttpRequest.readyState==4 && xmlHttpRequest.status ==200) "Success!"); var a=100; alert(a);}: alert("Failure!");

在jQuery 1.7.1源代码这两种简写形式太多了,如line 2643就有:

// Hook for boolean attributes
boolHook = {
  get: function( elem, name ) {
    // Align boolean attributes with corresponding properties
    // Fall back to attribute presence where some booleans are not supported
    var attrNode,
      property = jQuery.prop( elem, name );
    return property === true || 
typeof property !== "boolean" && ( attrNode = elem.getAttributeNode(name) ) && attrNode.nodeValue !== false "color: #ff00ff">看来还得继续学习进行总结。

以上这篇Javascript简写条件语句(推荐)就是小编分享给大家的全部内容了,希望能给大家一个参考,也希望大家多多支持。

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