Category: JavaScript

Sometimes, we want to format code with the pre tag in React and JSX.

In this article, we’ll look at how to format code with the pre tag in React and JSX.

Format Code with the pre Tag in React and JSX

To format code with the pre tag in React and JSX, we should put the code we want to display in template literals.

For instance, we can write:

import React from "react";

export default function App() {
  const foo = 1;
  const bar = '"a b   c"';

  return (
    <pre>{`
    var foo = ${foo};
    var bar = ${bar};
  `}</pre>
  );
}

We interpolate the foo and bar strings in the code template string.

All the spaces in the template string are preserved.

Conclusion

To format code with the pre tag in React and JSX, we should put the code we want to display in template literals.

Sometimes, we want to edit the value of multiple controlled input components in React.

In this article, we’ll look at how to edit the value of multiple controlled input components in React.

Edit Multiple Controlled Input Components’ Values in React

To edit the value of multiple controlled input components in React, we can create a function that returns the onChange callback for each input.

For instance, we can write:

import React, { useState } from "react";

export default function App() {
  const [contact, setContact] = useState({ firstName: "", lastName: "" });

  const handleChange = (propertyName) => (event) =>
    setContact((c) => ({ ...c, [propertyName]: event.target.value }));

  return (
    <div>
      <input
        type="text"
        onChange={handleChange("firstName")}
        value={contact.firstName}
      />
      <input
        type="text"
        onChange={handleChange("lastName")}
        value={contact.lastName}
      />
    </div>
  );
}

We have the contact state which is set to an object with the firstName and lastName properties as its initial value.

Then we create the handleChange function that takes propertyName and calls setContact to update the contact state’s propertyName property with the inputted value, which is stored in e.target.value .

Then we have 2 inputs with the value props set to each contact property.

And the onChange props are set to functions returned by handleChange with the propertyName to set the contact ‘s firstName or lastName property depending on the field.

Conclusion

To edit the value of multiple controlled input components in React, we can create a function that returns the onChange callback for each input.

Sometimes, we want to send multipart form data with Axios in a React component.

In this article, we’ll look at how to send multipart form data with Axios in a React component.

Send Multipart Form Data with Axios in a React Component

We can send form data with the FormData constructor.

We can pass that straight into the Axios post method.

For instance, we can write:

import React from 'react'
import axios, { post } from 'axios';

class App extends React.Component {

  constructor(props) {
    super(props);
    this.state ={
      file:null
    }
    this.onFormSubmit = this.onFormSubmit.bind(this)
    this.onChange = this.onChange.bind(this)
    this.fileUpload = this.fileUpload.bind(this)
  }

  onFormSubmit(e){
    e.preventDefault()
    const url = 'http://example.com/upload';
    const formData = new FormData();
    formData.append('file', this.state.file);
    const config = {
      headers: {
        'content-type': 'multipart/form-data'
      }
    }
    post(url, formData, config);
      .then((response) => {
        console.log(response.data);
      })
  }

  onChange(e) {
    this.setState({ file: e.target.files[0 ]})
  }

  render() {
    return (
      <form onSubmit={this.onFormSubmit}>
        <h1>File Upload</h1>
        <input type="file" onChange={this.onChange} />
        <button type="submit">Upload</button>
      </form>
   )
  }
}

We have a file input, where we set the file input to the file that’s submitted in the onChange method.

We save the selected file object as the value of the file state.

Then when we click the Upload button, onFormSubmit is run.

In the method, we created a FomrData instance.

Then we append our file into the FormData instance.

We also set the header so that we indicate that we’re sending form data.

Once we did that, we proceed with our file upload.

Conclusion

We can send form data with the FormData constructor.

We can pass that straight into the Axios post method.

React supports synthetic events in both the capturing and bubbling phases.

Therefore, our click events are propagated to the parent elements unless we stop them from doing so explicitly.

So if we have:

<root>
  <div onClick={this.handleAllClickEvents}>
    <foo>
      <bar>
        <target />
      </bar>
    </foo>
  </div>
</root>

We can listen to click events from child component with the handleAllClickEvents method.

Within it, we can write:

handleAllClickEvents(event) {
  const target = event.relatedTarget;
  const targetId = target.id;
  switch(targetId) {
    case 'foo':
      //...
    case 'bar':
      //...
  }
}

We get the click target with the event.relatedTarget property.

Then we get the click target’s ID with the id property.

Then we can check the IDs as we wish.

Difference Ways to Set the Initial State in a React Class Component

There’re multiple ways to set the initial state of a component in a class.

One way is standard and the other isn’t.

The standard way would be:

class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      name: 'james'
    }
  }

  render() {
    return  <div>{this.state.name}</div>
  }
}

We set it in the constructor with the this.state assignment.

The non-standard way is:

class App extends Component {
  state = {
    name: 'John'
  }

  render() {
    return  <div>{this.state.name}</div>
  }
}

This isn’t standard JavaScript syntax.

However, we can use it with TypeScript or a Babel plugin to transform it back to standard JavaScript.

This also sets the this.state instance variable.

Pass Props to a Component Passed as a Prop

If we want to pass props to a component that has been passed in as a prop, then we need to clone with the React.cloneElement method.

For instance, we can write:

const GrandChild = props => <div>{props.count}</div>;

class Child extends React.Component{
  constructor(){
    super();
    this.state = { count: 1 };
    this.updateCount= this.updateCount.bind(this);
  }

  updateCount(){
    this.setState(prevState => ({ count: prevState.count + 1 }))
  }

  render(){
    const Comp = this.props.comp;
    return (
      <div>
        {React.cloneElement(Comp, { count: this.state.count })}
        <button onClick={this.updateCount}>+</button>
      </div>
    );
  }
}

class Parent extends React.Component{
  render() {
    return(
      <Child comp={<GrandChild />} />
    )
  }
}

We have the GrandChild component which displays the count prop.

Then we have the Child prop to let us update the count state.

We pass that into the component that’s been passed in from the comp prop with React.cloneElement .

We got to clone it so that we return a version of the component that’s writable.

The 2nd argument has the prop name and value that we want to pass in respectively.

Sometimes, we want to send multipart form data with Axios in a React component.

In this article, we’ll look at how to send multipart form data with Axios in a React component.

Send Multipart Form Data with Axios in a React Component

We can send form data with the FormData constructor.

We can pass that straight into the Axios post method.

For instance, we can write:

import React from 'react'
import axios, { post } from 'axios';

class App extends React.Component {

  constructor(props) {
    super(props);
    this.state ={
      file:null
    }
    this.onFormSubmit = this.onFormSubmit.bind(this)
    this.onChange = this.onChange.bind(this)
    this.fileUpload = this.fileUpload.bind(this)
  }

  onFormSubmit(e){
    e.preventDefault()
    const url = 'http://example.com/upload';
    const formData = new FormData();
    formData.append('file', this.state.file);
    const config = {
      headers: {
        'content-type': 'multipart/form-data'
      }
    }
    post(url, formData, config);
      .then((response) => {
        console.log(response.data);
      })
  }

  onChange(e) {
    this.setState({ file: e.target.files[0 ]})
  }

  render() {
    return (
      <form onSubmit={this.onFormSubmit}>
        <h1>File Upload</h1>
        <input type="file" onChange={this.onChange} />
        <button type="submit">Upload</button>
      </form>
   )
  }
}

We have a file input, where we set the file input to the file that’s submitted in the onChange method.

We save the selected file object as the value of the file state.

Then when we click the Upload button, onFormSubmit is run.

In the method, we created a FomrData instance.

Then we append our file into the FormData instance.

We also set the header so that we indicate that we’re sending form data.

Once we did that, we proceed with our file upload.

Conclusion

We can send form data with the FormData constructor.

We can pass that straight into the Axios post method.