Warning: Unreachable code , using Reactjs

问题:

I am using ReactJs. I have two Components,PrescriptionIndex and PrescriptionNew, integrating one with another.

This is my first component 'PrescriptionNew'

import React, { Component } from 'react';
import FloatingActionButton from 'material-ui/FloatingActionButton';
import ContentAdd from 'material-ui/svg-icons/content/add';
import MuiThemeProvider from 'material-ui/styles/MuiThemeProvider'

class PrescriptionNew extends Component {

  render(){
    return(
      <div>
        <MuiThemeProvider>
          <FloatingActionButton mini={true} style={{"color": "pink"}}>
            <ContentAdd/>
          </FloatingActionButton>
        </MuiThemeProvider>
      </div>
    )
  }
}

export default PrescriptionNew;

This is my another Component "PrescriptionIndex"

import React , { Component } from 'react';
import { connect } from "react-redux";
import { fetchPrescriptionFromUrl } from '../actions/index.js';
import { Link } from 'react-router';
import PrescriptionNew from './new.jsx';
import '../app.css';

class PrescriptionIndex extends Component {

  componentDidMount(){
    this.props.fetchData(PORT+'/prescriptions');
  }

  render() {
    if (this.props.has_error){
      return(<p> Fetching an Api results in error</p>)
    }

    if (this.props.has_loading){
      return(<p> Loading...</p>)
    }
    if (this.props.prescriptions.prescriptions !== undefined) {
      return this.props.prescriptions.prescriptions.map(function(data){
        return (
          <div className="image-prescription" key={data.id}>
            <Link to={"/update/" + data.id} >
              <img src={data.image_path.image_path.url} 
                className="prescription-image"
                alt="prescription" 
              />
            </Link>  
          </div>      
        );
      });
    } else {
      return null;
    }
    return(
      <div>
        <PrescriptionNew /> //this is where I need my another component
      </div>
    )
  }
}
export default PrescriptionIndex;

On Running, the "PrescriptionNew" component is not visible. On examing the console, warning is stated as " Unreachable code". I have gone through other solutions, but I cannot able to study whats going wrong in my code.

回答1:

The reason is pretty straight forwards, you have an if-else and you are returning from both of them so the last part of your code is unreachable

you might want this

import React , { Component } from 'react';
import { connect } from "react-redux";
import { fetchPrescriptionFromUrl } from '../actions/index.js';
import { Link } from 'react-router';
import PrescriptionNew from './new.jsx';
import '../app.css';

class PrescriptionIndex extends Component {

  componentDidMount(){
    this.props.fetchData(PORT+'/prescriptions');
  }

  render() {
    if (this.props.has_error){
      return(<p> Fetching an Api results in error</p>)
    }

    if (this.props.has_loading){
      return(<p> Loading...</p>)
    }
    return(
      <div>
        <PrescriptionNew /> 
        {this.props.prescriptions.prescriptions && this.props.prescriptions.prescriptions.map(function(data){
        return (
          <div className="image-prescription" key={data.id}>
            <Link to={"/update/" + data.id} >
              <img src={data.image_path.image_path.url} 
                className="prescription-image"
                alt="prescription" 
              />
            </Link>  
          </div>      
        );
      }); }
      </div>
    )
  }
}
export default PrescriptionIndex;

回答2:

Your code is currently

if (X)
  return A
else
  return B
return C

Of course C is unreachable here. I think you meant to drop the else case (B) where you currently are returning null, and return C instead of it.

if (this.props.prescriptions.prescriptions !== undefined) {
  return this.props.prescriptions.prescriptions.map(function(data){
    return (
      <div className="image-prescription" key={data.id}>
        <Link to={"/update/" + data.id} >
          <img src={data.image_path.image_path.url} 
            className="prescription-image"
            alt="prescription" 
          />
        </Link>  
      </div>      
    );
  });
} else {
  // return null; <== remove this
  return (
    <div>
      <PrescriptionNew />
    </div>
  )
}