如何避免JavaScript中的全局變量

Question

如何避免在JavaScript中使用全局變量？

//load more 
    var size_li = $("#myList li").size(); 
    var x = 3; 
    $('#myList li:lt(' + x + ')').show(); 
    $('.loadmore').on('click', function() { 
     x = (x + 2 <= size_li) ? x + 2 : size_li; 
     $('#myList li:lt(' + x + ')').show(); 
    }); 

Answer 1

一個很好的技術，因爲這是一個自動執行的閉合：

// bob is a global variable, which you want to avoid 
var bob = 1; 

// By wrapping this function declaration in parentheses, then 
// appending(), it gets invoked immediately. But everything 
// inside it is scoped to the anonymous function! 
(function() { 
    // sue can only be seen inside this function 
    var sue = 1; 

    // But if you want to, you can still create global variables. 
    // This creates a global variable called joe: 
    window.joe = 1; 
})(); 

將這種技術應用到你的代碼中，你可以寫這個沒有全局變量：

(function() { 
    var size_li = $("#myList li").size(); 
    var x = 3; 

    $('#myList li:lt(' + x + ')').show(); 
    $('.loadmore').on('click', function() { 
     x = (x + 2 <= size_li) ? x + 2 : size_li; 
     $('#myList li:lt(' + x + ')').show(); 
    }); 
})(); 

Answer 2

我知道的方法是在ES6，這「讓我們可以定義裏面塊可變

如：

var b = 5 
{ 
let a = 10 
} 
a//undefine 
b// is 5