if else

var lemonChicken = false;
var beefWithBlackBean = true;
var sweetAndSourPork = true;
if(lemonChicken){
  console.log("1");
} else if (beefWithBlackBean) {
  console.log("2");
} else if (sweetAndSourPork) {
  console.log("3")  
}  else {
  console.log("4");
}

用return提前跳出函數

只要 JavaScript 解釋器在函數中遇到 return,它就會跳出函數,即使函數體中還有代碼沒有執行。

var fifthLetter = function (name) {
    if(name.length < 5){
        return;
    }
    return "The fifth letter of your name is " + name;
};
>>  undefined
fifthLetter("he");
>>  undefined
fifthLetter("hehehe");
>>  "The fifth letter of your name is hehehe"

使用多個return語句來代替if...else語句

var socreResult=function(score){
    if(score<3){
        return "小于3";
    }

    if(score<7){
        return "kk3<=score<7";
    }

    return "大于等于7";
};
socreResult(2);
>>  "小于3"
socreResult(5);
>>  "kk3<=score<7"
socreResult(10);
>>  "大于等于7"