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## 變量



聲明變量必須加上 `var` 關鍵字.





Decision:
當你沒有寫 `var`, 變量就會暴露在全局上下文中, 這樣很可能會和現有變量沖突.
另外, 如果沒有加上, 很難明確該變量的作用域是什么, 變量也很可能像在局部作用域中, 很輕易地泄漏到 Document 或者 Window 中,
所以務必用 `var` 去聲明變量.










                    
                
        
                
            
        
                
    
                
    
                
        
                
    
                

                







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