CODEWITHSUNDEEP
javascriptreactjs
kenodek
kenodek

Reputation: 372

How can I stop render() function till all the state will be updated?

The code below will call render() function three times. Is there a way to wait till all the three properties in state will be updated and then call render() only once? Maybe I should use shouldComponentUpdate? I'm new to ReactJS. I don't know how it would look like. Any ideas?

import React from "react";

export default class MyClass extends React.Component {
  constructor() {
    super();
    this.state = {
      first: "value1",
      second: "value2",
      third: "value3"
    };
  }

  changeFirst() {
    setTimeout(() => {
      this.setState({ first: "somethingFirst" });
    }, 2000);
  }
  changeSecond() {
    setTimeout(() => {
      this.setState({ second: "somethingSecond" });
    }, 3500);
  }
  changeThird() {
    setTimeout(() => {
      this.setState({ third: "somethingThird" });
    }, 5000);
  }

  componentDidMount() {
    this.changeFirst();
    this.changeSecond();
    this.changeThird();
  }

  render() {
    return (
      <div>
        {console.log(this.state.first) +
          "\n" +
          console.log(this.state.second) +
          "\n" +
          console.log(this.state.third) +
          "\n"}{" "}
      </div>
    );
  }
}

Upvotes: 0

Views: 58

Answers (2)

Taki
Taki

Reputation: 17654

yes you can use shouldcomponentupdate

shouldComponentUpdate(nextProps, nextState){
    const { first, second, third } = this.state;
    if(first !== nextState.first && second !== nextState.second && third !== nextState.third){
        return true;
    }

    return false;
}

this will prevent the component from updating unless the three state entires are updated.

Upvotes: 2

Silvio Biasiol
Silvio Biasiol

Reputation: 953

You can simply exit from the render function until all three variables are set:

import React from "react";

export default class MyClass extends React.Component {
    constructor() {
        super();
        this.state = {
            first: "",
            second: "",
            third: ""
        };
    }

    changeFirst() {
        setTimeout(() => {
            this.setState({ first: "somethingFirst" });
        }, 2000);
    }
    changeSecond() {
        setTimeout(() => {
            this.setState({ second: "somethingSecond" });
        }, 3500);
    }
    changeThird() {
        setTimeout(() => {
            this.setState({ third: "somethingThird" });
        }, 5000);
    }

    componentDidMount() {
        this.changeFirst();
        this.changeSecond();
        this.changeThird();
    }

    render() {
        if (!first || !second || !third) return (<div> Loading the vars... </div>)
        return (
            <div>
                {console.log(this.state.first) +
                    "\n" +
                    console.log(this.state.second) +
                    "\n" +
                    console.log(this.state.third) +
                    "\n"}{" "}
            </div>
        );
    }
}

Upvotes: 0

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