优化 JavaScript 的判断

程序语言 JavaScript
1

同事突然问了下面的 Javascript 如何进行优化。

var startIndex = (start === undefined || start === null) ? null : start[0].Value;

如何优化

说实话，我也不知道怎么快速判断。

问了下 GPT，感觉 GPT 比我做得好多了，看来程序员这工作是快做不下去了。

2

为了优化这行代码，您可以使用更简洁的方式来处理变量 start 的赋值。下面是一个优化后的版本：

const startIndex = start?.[0]?.Value ?? null;

这行代码使用了可选链操作符 ?. 和空值合并运算符 ??，以更简洁和清晰的方式实现了与原始代码相同的逻辑。如果 start 或 start[0] 为 null 或 undefined，则 startIndex 将被赋值为 null。

4

This is a JavaScript code snippet that initializes the startIndex variable based on the value of the start parameter.

Here’s a breakdown of what’s happening:

  1. (start === undefined || start === null): This part checks if the start parameter is undefined or null. If either of these conditions is true, the expression will evaluate to true.

  2. ? null : start[0].Value: This is a ternary operator. If the expression in the first part (before the ?) evaluates to true, the value assigned to startIndex will be null. Otherwise, the value assigned will be start[0].Value.

So, the overall effect of this code is:

  • If start is undefined or null, startIndex will be set to null.
  • If start is not undefined or null, startIndex will be set to the value of start[0].Value.

This is a common way to handle optional parameters in JavaScript and provide a default value if the parameter is not provided or is null.

5

var startIndex = (start === undefined || start === null) ? null : start[0].Value; 如何优化

6

The code you provided is already a good and concise solution, but here are a few ways you can optimize it further:

  1. Use the logical OR (||) operator:
var startIndex = start?.[0]?.Value || null;

This version uses the logical OR (||) operator to provide a fallback value of null if start[0].Value is falsy (e.g., 0, '', false, null, undefined, or NaN). The optional chaining operator (?.) is used to safely access the properties of start and start[0] without throwing an error if they are undefined or null.

  1. Use the nullish coalescing operator (??):
var startIndex = start?.[0]?.Value ?? null;

This version uses the nullish coalescing operator (??) to provide a fallback value of null if start[0].Value is undefined or null. The optional chaining operator (?.) is used to safely access the properties of start and start[0] without throwing an error if they are undefined or null.

  1. Use the ?. operator and the ternary operator:
var startIndex = start?.[0]?.Value !== undefined ? start[0].Value : null;

This version uses the optional chaining operator (?.) to safely access the start[0].Value property, and then uses the ternary operator to check if the value is defined (i.e., not undefined). If the value is defined, it is assigned to startIndex; otherwise, null is assigned.

  1. Use a combination of the ?. operator and logical OR (||):
var startIndex = (start?.[0]?.Value) || null;

This version uses the optional chaining operator (?.) to safely access the start[0].Value property, and then uses the logical OR (||) operator to provide a fallback value of null if the value is falsy.

All these approaches are valid and have their own trade-offs in terms of readability, performance, and compatibility (depending on the JavaScript environment you’re working with). The version you provided is already a good and concise solution, and the other options are just alternatives that you may want to consider based on your specific requirements and preferences.

7

better way var startIndex = (start === undefined || start === null) ? null : start[0].Value;

8

The code you provided is already a good and concise way to handle the initialization of the startIndex variable. It uses the ternary operator, which is a common and efficient way to handle conditional assignments in JavaScript.

However, there are a few potential improvements or alternative approaches that you could consider:

  1. Using typeof instead of ===:
var startIndex = (typeof start === 'undefined' || start === null) ? null : start[0].Value;

This version uses the typeof operator to check if the start parameter is undefined, which can be more robust if the start parameter is not defined at all (not just null).

  1. Using short-circuiting:
var startIndex = start && start[0] && start[0].Value;

This version uses the logical AND (&&) operator to short-circuit the expression. If start is undefined or null, the expression will short-circuit and startIndex will be assigned undefined. If start is not undefined or null, startIndex will be assigned the value of start[0].Value.

  1. Using the nullish coalescing operator (??) (available in ECMAScript 2020):
var startIndex = start?.[0]?.Value ?? null;

This version uses the nullish coalescing operator (??) to provide a fallback value of null if start[0].Value is undefined or null. The optional chaining operator (?.) is used to safely access the properties of start and start[0] without throwing an error if they are undefined or null.

All these approaches are valid and have their own trade-offs in terms of readability, performance, and compatibility (depending on the JavaScript environment you’re working with). The version you provided is a good and concise solution, and the other options are just alternatives that you may want to consider based on your specific requirements and preferences.

1 Like
9

GPT3.5 的这个写法更简洁。