Dynamically Add CSS Classes to Item Rows

SlickGrid is very flexible and it allows you to change or add CSS Class(es) dynamically (or on page load) by changing it's Item Metadata (see SlickGrid Wiki - Item Metadata). There is also a Stack Overflow answer, which this code below is based from.

Demo

Demo Page / Demo Component

Dynamically Change CSS Classes

Component

const Example: React.FC = () => {
  const [dataset, setDataset] = useState<any[]>([]);
  const [columns, setColumns] = useState<Column[]>([]);
  const [options, setOptions] = useState<GridOption | undefined>(undefined);
  const reactGridRef = useRef<SlickgridReactInstance | null>(null);

  function reactGridReady(reactGrid: SlickgridReactInstance) {
    reactGridRef.current = reactGrid;
  }

  /**
   * Change the Duration Rows Background Color
   * You need to get previous SlickGrid DataView Item Metadata and override it
   */
  function changeDurationBackgroundColor() {
    reactGridRef.current?.dataView.getItemMetadata = updateItemMetadataForDurationOver50(reactGridRef.current?.dataView.getItemMetadata);

    // also re-render the grid for the styling to be applied right away
    reactGridRef.current?.slickGrid.invalidate();
    reactGridRef.current?.slickGrid.render();
  }

  /**
   * Override the SlickGrid Item Metadata, we will add a CSS class on all rows with a Duration over 50
   * For more info, you can see this SO https://stackoverflow.com/a/19985148/1212166
   */
  function updateItemMetadataForDurationOver50(previousItemMetadata: any) {
    const newCssClass = 'duration-bg';

    return (rowNumber: number) => {
      const item = reactGridRef.current?.dataView.getItem(rowNumber);
      let meta = {
        cssClasses: ''
      };
      if (typeof previousItemMetadata === 'object') {
        meta = previousItemMetadata(rowNumber);
      }

      // our condition to check Duration over 50
      if (meta && item && item.duration) {
        const duration = +item.duration; // convert to number
        if (duration > 50) {
          meta.cssClasses = (meta.cssClasses || '') + ' ' + newCssClass;
        }
      }

      return meta;
    };
  }

  return !options ? null : (
    <button class="btn btn-default" onClick={() => changeDurationBackgroundColor()}>Highlight Rows with Duration over 50</button>
    <SlickgridReact gridId="grid1"
      columnDefinitions={columns}
      gridOptions={options}
      dataset={dataset}
      onReactGridCreated={$event => reactGridReady($event.detail)}
    />
  );
}

On Page Load

Or if you want to apply the styling right after the page load

Component

const Example: React.FC = () => {
  const [dataset, setDataset] = useState<any[]>([]);
  const [columns, setColumns] = useState<Column[]>([]);
  const [options, setOptions] = useState<GridOption | undefined>(undefined);
  const reactGridRef = useRef<SlickgridReactInstance | null>(null);

  function reactGridReady(reactGrid: SlickgridReactInstance) {
    reactGridRef.current = reactGrid;
  
    // if you want to change background color of Duration over 50 right after page load,
    // you would put the code here, also make sure to re-render the grid for the styling to be applied right away
    reactGrid.dataView.getItemMetadata = updateItemMetadataForDurationOver50(reactGrid.dataView.getItemMetadata);
    reactGrid.slickGrid.invalidate();
    reactGrid.slickGrid.render();
  }

  /**
   * Change the SlickGrid Item Metadata, we will add a CSS class on all rows with a Duration over 50
   * For more info, you can see this SO https://stackoverflow.com/a/19985148/1212166
   */
  function updateItemMetadataForDurationOver50(previousItemMetadata: any) {
    const newCssClass = 'duration-bg';

    return (rowNumber: number) => {
      const item = reactGridRef.current?.dataView.getItem(rowNumber);
      let meta = {
        cssClasses: ''
      };
      if (typeof previousItemMetadata === 'object') {
        meta = previousItemMetadata(rowNumber);
      }

      if (meta && item && item.duration) {
        const duration = +item.duration; // convert to number
        if (duration > 50) {
          meta.cssClasses = (meta.cssClasses || '') + ' ' + newCssClass;
        }
      }

      return meta;
    };
  }
}