javascript - JavaScript Map.get（variableName）返回未定义(JavaScript Map.get(variableName) is returning undefined)

Question

I am using react router to pass an Id via the URL parameter and setting my variable like let { posterId } = useParams();(我正在使用let { posterId } = useParams(); Router通过URL参数传递ID，并设置我的变量，例如let { posterId } = useParams();)

This seems to be working as expected because I can write it out in the JSX just fine <h1> This is a specific poster {posterId}</h1>(这似乎按预期工作，因为我可以在JSX中将其写得很好<h1> This is a specific poster {posterId}</h1>) However, when I try to use it to get from a map that I am passing via props it returns undefined from the map props.postersMap.get(posterId) .(但是，当我尝试使用它来获取我通过props传递的地图时，它会从props.postersMap.get(posterId)返回未定义。) I verified that the map is populated and if I hard code the .get method to the variable value it works as expected.(我验证了是否填充了地图，并且如果将.get方法硬编码为变量值，则它可以按预期工作。) Is there something I am just overlooking?(有什么我可以忽略的吗？) Edit: full component code(编辑：完整的组件代码) import React from 'react' import { useParams} from 'react-router-dom' export default function Poster(props) { let { posterId } = useParams(); return ( <div> {console.log(props.postersMap)} {console.log(posterId)} {console.log(props.postersMap.get(posterId))} {props.postersMap.get(posterId) ? <p>{props.postersMap.get(posterId).band}</p> : <p></p>} </div> ) } Here is what my console.logs are showing(这是我的console.log显示的内容)   ask by Cogorlopez translate from so

Answer 1

The js Map keys must match exactly: if keys are numbers (and they are in your case), then you retrieve them using numeric values.(js Map键必须完全匹配：如果键是数字（在您的情况下是键），则可以使用数字值检索它们。)

props.postersMap.get(Number(posterId)) would do.(props.postersMap.get(Number(posterId))可以。) Or guarantee you're providing a valid numeric any other available way.(或保证您以任何其他可用的方式提供有效的数字。)