In an interview, I was asked the question as described in the title. I think the interviewer wanted to ask about the underlying principles of property accessors in js. So what I want to know is the perfemance and principles instead of difference.

在一次采访中，我被问到了标题中描述的问题。我想采访者想问的是js中属性访问器的基本原理。所以我想知道的是表现和原则，而不是区别。

Bracket Notation

方括号表示法

const a = { b: { c: 'Bracket Notation' } }
console.log(a['b']['c'])

Dot Notation

点号记法

const a = { b: { c: 'Dot Notation' } }
console.log(a.b.c)

One of the key differences between dot notation and bracket notation is in their ability to access dynamically generated properties.

点表示法和方括号表示法之间的主要区别之一是它们访问动态生成的属性的能力。

The dynamic property access capability is a significant advantage of bracket notation and is essential when you need to compute the property name at runtime. It allows you to access properties that you couldn't access using dot notation, such as properties with spaces or special characters, or properties whose names are stored in variables.

动态属性访问功能是方括号表示法的一个重要优势，当您需要在运行时计算属性名称时，它是必不可少的。它允许您访问不能使用点符号访问的属性，例如带有空格或特殊字符的属性，或者名称存储在变量中的属性。

Performance-wise, there used to be a minor difference between the two in older JavaScript engines, with dot notation being slightly faster. However, modern JavaScript engines have optimized both notations to a point where the difference is negligible.

在性能方面，在较旧的JavaScript引擎中，这两者之间曾经有一个微小的区别，点号表示法稍微快一些。然而，现代的JavaScript引擎已经对这两种表示法进行了优化，以至于差异可以忽略不计。

Dot Notation:

点符号：

Dot notation is more concise and easier to read.
It is the preferred way to access properties when you know the property name in advance.
Dot notation is generally faster because it's more optimized by JavaScript engines.

点符号更简洁、更易于阅读。当您预先知道属性名称时，这是访问属性的首选方式。点号表示法通常更快，因为它被Java引擎优化得更好。

var person = {
    name: 'John',
    age: 30
};

var name = person.name; // Using dot notation

Bracket Notation:

方括号表示法：

Bracket notation is more flexible because it allows you to access properties using dynamic property names or properties with spaces or special characters.
It is used when the property name is not known in advance and is stored in a variable.

括号表示法更加灵活，因为它允许您使用动态属性名称或带有空格或特殊字符的属性来访问属性。当事先不知道属性名称并存储在变量中时，使用它。

var person = {
    'first name': 'John',
    age: 30
};

var propName = 'age';
var age = person[propName]; // Using bracket notation with a variable

In terms of performance, dot notation is generally faster because it's optimized by JavaScript engines. However, the difference in performance is often negligible in most real-world scenarios, and you should prioritize code clarity and readability over micro-optimizations.

就性能而言，点符号通常更快，因为它是由JavaScript引擎优化的。然而，在大多数实际场景中，性能差异通常可以忽略不计，您应该优先考虑代码清晰度和可读性，而不是微优化。