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      为什么我可以在javascript中更改常量对象

      Why can I change a constant object in javascript(为什么我可以在javascript中更改常量对象)

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                本文介绍了为什么我可以在javascript中更改常量对象的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                问题描述

                我知道 ES6 还没有标准化,但是 很多浏览器目前都支持 const JS 中的关键字.

                I know that ES6 is not standardized yet, but a lot of browsers currently support const keyword in JS.

                在规范中是这样写的:

                常量的值不能通过重新赋值来改变,并且常量不能重新声明.正因为如此,虽然是可以在不初始化的情况下声明一个常量,它将是这样做没用.

                The value of a constant cannot change through re-assignment, and a constant cannot be re-declared. Because of this, although it is possible to declare a constant without initializing it, it would be useless to do so.

                当我做这样的事情时:

                const xxx = 6;
                xxx = 999;
                xxx++;
                const yyy = [];
                yyy = 'string';
                yyy = [15, 'a'];
                

                我看到一切正常 xxx 仍然是 6yyy[].

                I see that everything is ok xxx is still 6 and yyy is [].

                但是如果我这样做 yyy.push(6);yyy.push(1);,我的常量数组变了.现在它是 [6, 1] 顺便说一句,我仍然无法用 yyy = 1; 更改它.

                But if I do yyy.push(6); yyy.push(1);, my constant array has been changed. Right now it is [6, 1] and by the way I still can not change it with yyy = 1;.

                我这是一个错误,还是我遗漏了什么?我在最新的 chrome 和 FF29 中试了一下

                I this a bug, or am I missing something? I tried it in the latest chrome and FF29

                推荐答案

                文档说明:

                ...常数不能通过重新赋值来改变
                ...常量不能重新声明

                ...constant cannot change through re-assignment
                ...constant cannot be re-declared

                当您添加到数组或对象时,您并没有重新分配或重新声明常量,它已经被声明和分配,您只是添加到常量指向的列表"中.

                When you're adding to an array or object you're not re-assigning or re-declaring the constant, it's already declared and assigned, you're just adding to the "list" that the constant points to.

                所以这很好用:

                const x = {};
                
                x.foo = 'bar';
                
                console.log(x); // {foo : 'bar'}
                
                x.foo = 'bar2';
                
                console.log(x); // {foo : 'bar2'}  
                

                还有这个:

                const y = [];
                
                y.push('foo');
                
                console.log(y); // ['foo']
                
                y.unshift("foo2");
                
                console.log(y); // ['foo2', 'foo']
                
                y.pop();
                
                console.log(y); // ['foo2']
                

                但这些都不是:

                const x = {};
                x = {foo: 'bar'}; // error - re-assigning
                
                const y = ['foo'];
                const y = ['bar']; // error - re-declaring
                
                const foo = 'bar'; 
                foo = 'bar2';       // error - can not re-assign
                var foo = 'bar3';   // error - already declared
                function foo() {};  // error - already declared
                

                这篇关于为什么我可以在javascript中更改常量对象的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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