存储在堆栈上的 Javascript 字符串
我正在阅读 面向 Web 开发人员的专业 JavaScript 第 3 版. 在第 4 章的总结中可以阅读:
I'm reading Professional JavaScript for Web Developers 3rd ed. and in the summary of chapter 4 one can read:
两种类型的值可以存储在 JavaScript 变量中:原始值和引用值.原始值具有以下五种原始数据类型之一:Undefined、Null、Boolean、Number 和 String.原始值和参考值具有以下特点:
Two types of values can be stored in JavaScript variables: primitive values and reference values. Primitive values have one of the five primitive data types: Undefined, Null, Boolean, Number, and String. Primitive and reference values have the following characteristics:
- 原始值具有固定大小，因此存储在堆栈的内存中.
但我可以有不同的字符串，比如:
But I can have different strings, say:
var a = "ABC";
var a = "ABC";
//或
var b = "一些非常烦人的长字符串..."
var b = "Some very irritatingly long string..."
它们的大小明显不同，那么如何在堆栈上分配它们呢?
They clearly differ in size, so how can they be allocated on the stack?
我相信关于数字也可以问同样的问题...
I believe the same question can be asked about numbers...
所以我肯定在这里遗漏了一些重要的东西.
So I am for sure missing something important here.
谁能解释一下为什么字符串/数字是固定大小的以及如何将它们存储在堆栈上?
Can someone explain why strings/numbers are of fixed size and how they can be stored on stack?
推荐答案
字符串(通常是数字)不是固定大小的，也不是完整地存储在堆栈中，而是在语言中表现得好像它们可以存储在堆栈中.
Strings (and usually numbers) are not of fixed size, and are not stored in their entirety on the stack, but within the language they behave as if they could be stored on the stack.
由实现语言的人决定如何在内部存储数据.通常数据会根据值以不同的方式存储.
It's up to the one implementing the language to decide how to store the data internally. Often the data is stored in different ways depending on the value.
虽然 JavaScript 中的数字始终表现为双精度浮点数，但通常当数字恰好是整数值时，它们的存储方式会有所不同.一些 JavaScript 引擎使用未使用的双精度值作为整数值，其他一些将整数存储在值本身中，将双精度值存储在堆中.
Although numbers in JavaScript always behave as double precision floating point numbers, usually numbers are stored differently when they happen to be integer values. Some JavaScript engines uses unused double values as integer values, some others store integers in the value itself and double values on the heap.
对于字符串，一些数据可以存储在堆栈上的一个项目中，例如长度和对存储在堆上的字符串内容的引用.对于短字符串，字符可以代替引用放入堆栈中的值中，因此不需要堆上的额外数据.
For strings some of the data can be stored in an item on the stack, for example the length and a reference to the string content stored on the heap. For short strings the characters could fit in the value in the stack in place of the reference, and thus need no extra data on the heap.
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