Development Tips for React Developers

Anil Kumar

Mar 15, 2020·3 min read

1. Updating an object with setState in React

> For example

Given the state ,

this.state = {jasper:{name: 'jasper', age:28}}

You can update an object using 2 methods

1. Object.assign()
2. Spread Operator …

1 > Object.assign

this.setState(prevState => {
    let jasper = Object.assign({}, prevState.jasper)
    jasper.name = 'someothername'
    return { jasper }
})

2 > Spread Operator

this.setState(prevState => ({
    jasper: { ...prevState.jasper,
     name: 'something'
    }
}))

2. Updating a nested object in React

• Object.assign & Spread Operator creates only shallow copy

> For example

Given the nested object ,

this.state = {
   "food":{
      "sandwich":{
         "capsicum":true,
         "crackers":true,
         "mayonnaise":true
      },
      "pizza":{
         "jalapeno":true,
         "extraCheese":false
      }
   }
}

• update extraCheese of Pizza object (using Spread Operator)

> Spread Operator for nested object

this.setState(prevState => (
{
   "food":{
      "...prevState.food",
      "pizza":{
         "...prevState.food.pizza",
         "extraCheese":true
      }
   }
})
)

3. Deploy App on a subdirectory

• If you want to deploy App on a Subdirectory such as

https://myapp.com/directory-name

You can deploy app on a subdirectory using 2 methods

1. Set the base name basename
2. Set the app homepage in package.json

1 > Set the base name

<Router basename={'/directory-name'}> 
 <Route path='/' component {Home} />
  ...
</Router>

• Setting the basename attribute on the <Router /> component tells React Router that the app will be served from a subdirectory

2 > Set the app homepage in package.json

• In package.json file, set the property homepage
• npm run build command comes from creact-react-app and npm run build use homepage property to make sure the production build points to the correct location
• By default, CRA (Create React App) produces a build assuming your app is hosted at the server root
• To override this, specify the homepage in your packge.json

"homepage" : "http://mywebsite.com/relativepath"

4. Render nested object

• Sometimes, you will find the data in nested object type
• Object is NOT so easy to iterate compared to array in JavaScript. So I recommend you to convert the object into an array using Object.keys() method

Given the nested object,

const fruits = {
   "apple":{
      "price":10,
      "weight":2.5,
      "color":"red"
   },
   "banana":{
      "price":5,
      "weight":1.2,
      "color":"yellow"
   }
}

> Object.keys() and use the key to map

render() {
  Object.keys(fruits).map(function(fruit_name){
    return(
       <tr key={fruit_name}>
        <tr>
          <td>
           <b> Template: {fruit_name} </b>
          </td>
        </tr>
        {fruits[fruit_name].items.map(function(item){
          return(
            <tr key={item.id}>
              <td>{item}</td>
            </tr>
           )
           })}
         </tr>
       )
  })
}

5. Simple nested Mapping

const mscList = classroomSummary.map((classRoom, ind) => (
         classRoom.map(classData => (
           <MSCItem classData={classData} />
          ))
  ))

6. Detect Route Change

• For many times, you will find a needs to detect route change and do something (i.e., change the state “loading” into false whenever there is a page refresh or route change)
• To detect route change in React, you need to use listen method in history property

For example,

• I want to change my state expanded to false whenever there is a route change

> listen method in history property

constructor(props){
  super(props);
    this.props.history.listen((location, action) => {
     // console.log('history changed')
     this.routeChange();
  })
}
// routeChange function
routeChange = () => {
  const { BaseActions } = this.props
  BaseActions.sideBar({expanded: false})
}

7. history push INSTEAD OF window.location

• The main difference between history.push and window.location is that

// CLIENT SIDE
history.push('/')// SERVER SIDE
window.location('/')

• Use history API history.push('/') to refresh the page for a better UX

8. Query String

• Query String is often used for passing parameters (data) around both in CLIENT & SERVER side
• Installation — npm install query-string
• I used Query String to filter data using the selected options
• For example, if a user choose Europe , I pass Europe as a queryString ...URL...?Region=Europe and filter the data using the value of Region in URL

> query string

• push the state or props to URL using history.push method

resetBtn = () => {
  const { history, schoolid, 
          selectedAgeValue, selectedDomain } = this.props;   history.push(`/reports/disadmin/${schoolid}
    ?age=${selectedAgeValue}&domain=${selectedDomain}`)
}

• then use it using queryString (e.g., queryString.parse method
• In this example, I get the values for key age & domain and update Redux

import queryString from 'query-string'const params = queryString.parse(window.location.search)const param_selectedAgeValue = params.ageconst param_selectedDomain = params.domainreturn state.set('param_selectedAgeValue', param_selectedAgeValue)