JavaScript with用法

    function students() {  
            this.name = 'Jerry';  
            this.age  = 18;  
            this.score = function(yuwen,shuxue,waiyu) {  
                return yuwen + shuxue + waiyu;  
            }  
        }  
      
      
        stu = new students();  
      
      
        //一般的寫法  
        stu.name = 'Jack';  
        stu.age = 28;  
        console.log("name : " + stu.name + ", age: " + stu.age + ", score : " + stu.score(85,90,92));  
      
      
        //使用with後，就相當於作用域此對象了  
        with(stu) {  
            name = 'tom';  
            age = 23;  
            console.log("name : " + name + ", age: " + age + ", score : " + score(60,80,50));  
        }  

<form onclick="return validForm(this);">
   <input type="text" name="username" id="username"/>
   <input type="submit"/>
</form>

//驗證個表單
    //一般寫的方式
    function validForm1(formObj) {
        if(formObj.username.value == '') {
            console.log('username can not null.');
            return false;
        }
    }


    //加入with後
    function validForm(formObj) {
        with(formObj) {
            if(username.value == '') {
                console.log('username can not null.');
                return false;
            }
        }
    }