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To run the imagesrore function onload I have to call <img src="https://stackoverflow.com/questions/54820064/image_7.jpg" className="hide" alt="image_7.jpg"/> image but actually there is no use of this line and if I remove this onload doesn't work and function is not called. So how can I call the imagestore() onload in react.

class PicturesList extends React.Component {
        constructor(props) {
          super(props);
          this.state = {
          imagesarray: []
          };
          this.imagestore = this.imagestore.bind(this);
        }
        render() {
          return (
          <div>
            <div onLoad= {() => this.imagestore()}>
                <img src="image_7.jpg" className="hide" alt="image_7.jpg"/>
                // To run the imagesrore function onload I have to call this image but actually there is no use of this line and if I remove this onload doesn't work and function is not called
            </div>
            <Gallery url={this.state.imagesarray}/>
          </div>
          );
        }
        imagestore()
        {
        const imgUrls=this.props.apikeys;
        const objarr = Object.values(imgUrls);
        this.setState({
            imagesarray: objarr
        });
        }

      }

what I want

class PicturesList extends React.Component {
            constructor(props) {
              super(props);
              this.state = {
              imagesarray: []
              };
              this.imagestore = this.imagestore.bind(this);
            }
            render() {
              return (
              <div>
                <div onLoad= {() => this.imagestore()}>

                    // but when I did this imagestore() function not called
                </div>
                <Gallery url={this.state.imagesarray}/>
              </div>
              );
            }
            imagestore()
            {
            const imgUrls=this.props.apikeys;
            const objarr = Object.values(imgUrls);
            this.setState({
                imagesarray: objarr
            });
            }

          }

Answers

Instead of rendering the image which you dont want, you could simply load it in componentDidMount like

class PicturesList extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
      imagesarray: []
      };
      this.imagestore = this.imagestore.bind(this);
    }

    componentDidMount() {
       const img = new Image();
        img.onload =() => {
          // image  has been loaded
          this.imagestore()
        };

        img.src = 'image_7.jpg';
    }
    render() {
       return (
          <div>
            </div>
            <Gallery url={this.state.imagesarray}/>
          </div>
       );
    }
    imagestore() {
        const imgUrls=this.props.apikeys;
        const objarr = Object.values(imgUrls);
        this.setState({
            imagesarray: objarr
        });
    }

}

The above solution is just to call imageStore once an image is loaded. However if what you intend is to call imageStore when the component has fully loaded,just trigger this.imageStore() in componentDidMount

class PicturesList extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
      imagesarray: []
      };
      this.imagestore = this.imagestore.bind(this);
    }

    componentDidMount() {
        this.imagestore()
    }
    render() {
       return (
          <div>
            </div>
            <Gallery url={this.state.imagesarray}/>
          </div>
       );
    }
    imagestore() {
        const imgUrls=this.props.apikeys;
        const objarr = Object.values(imgUrls);
        this.setState({
            imagesarray: objarr
        });
    }

}