In computer programming, lint is a Unix utility that flags some suspicious and non-portable constructs (likely to be bugs) in C language source code; generically, lint or a linter is any tool that flags suspicious usage in software written in any computer language. The term lint-like behavior is sometimes applied to the process of flagging suspicious language usage. Lint-like tools generally perform static analysis of source code.
Did the navigation start successfully? Has the server responded?
导航是否成功启动？服务器响应了吗？
Is it useful?
是有用的么
Has enough content rendered that users can engage with it?
是否渲染了足够的内容给用户？
Is it usable?
可以使用了么
Can users interact with the page, or is it busy?
用户可以与页面进行交互，还是页面仍在忙碌中？
Is it delightful?
流畅么
Are the interactions smooth and natural, free of lag and jank?
交互是否流畅，没有延迟和卡顿？
如何度量
通过实验环境进行测试
通过实际生产环境进行测试
指标类型
感知的加载速度：页面加载并将其所有可视元素呈现到屏幕的速度。
加载响应度：页面加载和执行任何必需的JavaScript代码以使组件快速响应用户交互的速度
运行时响应性：页面加载后，页面对用户交互的响应速度有多快。
视觉稳定性：页面上的元素是否会造成用户不期望的方式移动，并可能干扰他们的交互？
平滑度：过渡和动画是否以一致的帧速率渲染并从一种状态流畅地流动到另一种状态？
重要的衡量指标
First contentful paint (FCP): measures the time from when the page starts loading to when any part of the page’s content is rendered on the screen. (lab, field)
第一个内容的绘制：测量从页面开始加载到屏幕上呈现页面内容的任意部分的时间。
Largest contentful paint (LCP): measures the time from when the page starts loading to when the largest text block or image element is rendered on the screen. (lab, field)
最大内容的绘制：测量从页面开始加载到屏幕上最大的文本块或图像元素被渲染的时间。
First input delay (FID): measures the time from when a user first interacts with your site (i.e. when they click a link, tap a button, or use a custom, JavaScript-powered control) to the time when the browser is actually able to respond to that interaction. (field)
Time to Interactive (TTI): measures the time from when the page starts loading to when it’s visually rendered, its initial scripts (if any) have loaded, and it’s capable of reliably responding to user input quickly. (lab)
Total blocking time (TBT): measures the total amount of time between FCP and TTI where the main thread was blocked for long enough to prevent input responsiveness. (lab)
To provide a good user experience, sites should strive to have First Contentful Paint occur within 1 second of the page starting to load. To ensure you’re hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
LCP：2.5秒内
To provide a good user experience, sites should strive to have Largest Contentful Paint occur within the first 2.5 seconds of the page starting to load. To ensure you’re hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
FID：100毫秒以内
To provide a good user experience, sites should strive to have a First Input Delay of less than 100 milliseconds. To ensure you’re hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
TTI：5秒内
To provide a good user experience, sites should strive to have a Time to Interactive of less than 5 seconds when tested on average mobile hardware.
TBT：300毫秒以内
To provide a good user experience, sites should strive to have a Total Blocking Time of less than 300 milliseconds when tested on average mobile hardware.
CLS：分数小于0.1
To provide a good user experience, sites should strive to have a CLS score of less than 0.1. To ensure you’re hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
