JavaScript Data GridCell Renderer

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By default the grid will create the cell values using simple text. If you want more complex HTML inside the cells you can achieve this using Cell Renderers.

The example below uses a Cell Renderer to render a hash (#) symbol for each medal won (instead of the medal count), and a cell with a button in the Total column:

Cell Renderer Component

The interface for the cell renderer component is as follows:

interface ICellRendererComp {
    // Optional - Params for rendering. The same params that are passed to the cellRenderer function.
    init?(params: ICellRendererParams): void;

    // Mandatory - Return the DOM element of the component, this is what the grid puts into the cell
    getGui(): HTMLElement;

    // Optional - Gets called once by grid after rendering is finished - if your renderer needs to do any cleanup,
    // do it here
    destroy?(): void;

    // Mandatory - Get the cell to refresh. Return true if the refresh succeeded, otherwise return false.
    // If you return false, the grid will remove the component from the DOM and create
    // a new component in its place with the new values.
    refresh(params: ICellRendererParams): boolean;
}

The interface for the cell renderer parameters is as follows:

Registering Cell Renderers with Columns

See the section registering custom components for details on registering and using custom Cell Renderers.

Component Refresh

Component Refresh needs a bit more explanation. Here we go through some of the finer details.

Events Causing Refresh

The grid can refresh the data in the browser, but not every refresh / redraw of the grid results in the refresh method of your cell renderer getting called. The following items are those that do cause refresh to be called:

• Calling rowNode.setDataValue(colKey, value) to set a value directly onto the rowNode. This is the preferred API way to change one value from outside of the grid.
• When editing a cell and editing is stopped, so that cell displays new value after editing.
• Calling api.refreshCells() to inform grid data has changed (see Refresh).

If any of the above occur and the grid confirms the data has changed via Change Detection, then the refresh() method will be called.

The following will not result in the cell renderer's refresh method being called:

• Calling rowNode.setData(data) to set new data into a rowNode. When you set the data for the whole row, the whole row in the DOM is recreated again from scratch.
• Scrolling the grid vertically causes columns (and their containing cells) to be removed and inserted due to column virtualisation.

All of the above will result in the component being destroyed and recreated.

Grid vs Component Refresh

The refresh method returns back a boolean value. If you do not want to handle the refresh in the cell renderer, just return back false from an otherwise empty method. This will indicate to the grid that you did not refresh and the grid will instead destroy the component and create another instance of your component from scratch instead.

The example below demonstrates handling the refresh, where the Gold, Silver and Bronze column cell renderers refresh when the Update Data button is clicked.

Change Detection

As mentioned in the section on Change Detection, the refresh of the Cell will not take place if the value getting rendered has not changed.

Cell Renderer Component Lifecycle

The lifecycle of the cell renderer is as follows:

• new is called on the class.
• init() is called once.
• getGui() is called 0 or 1 times (destroy could get called first, i.e. when scrolling quickly)
• refresh() is called 0...n times (i.e. it may never be called, or called multiple times)
• destroy() is called once.

In other words, new(), init() and destroy() are always called exactly once. getGui() will typically get called once unless destroy() is called first. refresh() is optionally called multiple times.

If you are doing refresh(), remember that getGui() is only called once (assuming the cell renderer hasn't been destroyed first), so be sure to update the existing GUI in your refresh, do not think that the grid is going to call getGui() again to get a new version of the GUI.

Cell Rendering Flow

The diagram below (which is taken from the section Cell Content) summarises the steps the grid takes while working out what to render and how to render.

In short, a value is prepared. The value comes using either the colDef.field or the colDef.valueGetter. The value is also optionally passed through a colDef.valueFormatter if it exists. Then the value is finally placed into the DOM, either directly, or by using the chosen colDef.cellRenderer.

Complementing Cell Renderer Params

On top of the parameters provided by the grid, you can also provide your own parameters. This is useful if you want to 'configure' your Cell Renderer. For example, you might have a Cell Renderer for formatting currency but you need to provide what currency for your cell renderer to use.

Provide params to a cell renderer using the colDef option cellRendererParams.

// define cellRenderer to be reused
const myCellRenderer = params => `<span style="color: ${params.color}">${params.value}</span>`;

// use with a colour
colDef.cellRenderer = myCellRenderer;
colDef.cellRendererParams = {
    color: 'guinnessBlack'
}

// use with another colour
colDef.cellRenderer = myCellRenderer;
colDef.cellRendererParams = {
    color: 'irishGreen'
}

Data in Cell Renderers

Sometimes the data property in the parameters given to a cell renderer might not be populated. This can happen for example when using row grouping (where the row node has aggData and groupData instead of data), or when rows are being loaded in the Infinite Row Model and do not yet have data. It is best to check that data does exist before accessing it in your cell renderer, for example:

colDef.cellRenderer = params => {
    // check the data exists, to avoid error
    if (params.data) {
        // data exists, so we can access it
        return `**${params.data.theBoldValue}**`;
    }
    // when we return null, the grid will display a blank cell
    return null;
};

Cell Renderer Function

Instead of using a component, it's possible to use a simple function for a cell renderer. The function takes the same parameters as the cell renderer init method in the component variant. The function should return back either a) a string of HTML or b) a DOM object.

Use the function variant of a cell renderer if you have no refresh or cleanup requirements (ie you don't need to implement the refresh or destroy functions).

Below are some simple examples of cell renderers provided as simple functions:

// put the value in bold
colDef.cellRenderer = params => `**${params.value.toUpperCase()}**`;

// put a tooltip on the value
colDef.cellRenderer = params => `<span title="the tooltip">${params.value}</span>`;

// create a DOM object
colDef.cellRenderer = params => {
    const eDiv = document.createElement('div');
    eDiv.innerHTML = '<span class="my-css-class"><button class="btn-simple">Push Me</button></span>';
    const eButton = eDiv.querySelectorAll('.btn-simple')[0];

    return eDiv;
}

Complex Cell Renderer Example

The example below shows five columns formatted, demonstrating each of the methods above.

• 'Month' column uses cellStyle to format each cell in the column with the same style.
• 'Max Temp' and 'Min Temp' columns uses the Function method to format each cell in the column with the same style.
• 'Days of Air Frost' column uses the Component method to format each cell in the column with the same style
• 'Days Sunshine' and 'Rainfall (10mm)' use simple functions to display icons.

Custom Group Cell Renderer Example

The example below demonstrates how to implement a simple custom group cell renderer.

• The example has a custom icon which represents whether the group is open
• Reacts to the row events if the group is expanded from another source
• Cleans up event listeners when it's disposed of

Accessing Cell Renderer Instances

After the grid has created an instance of a cell renderer for a cell it is possible to access that instance. This is useful if you want to call a method that you provide on the cell renderer that has nothing to do with the operation of the grid. Accessing cell renderers is done using the grid API getCellRendererInstances(params).

An example of getting the cell renderer for exactly one cell is as follows:

// example - get cell renderer for first row and column 'gold'
const firstRowNode = api.getDisplayedRowAtIndex(0);
const params = { columns: ['gold'], rowNodes: [firstRowNode] };
const instances = api.getCellRendererInstances(params);

if (instances.length > 0) {
    // got it, user must be scrolled so that it exists
    const instance = instances[0];
}

Note that this method will only return instances of the cell renderer that exists. Due to row and column virtualisation, renderers will only exist for cells that the user can actually see due to horizontal and vertical scrolling.

The example below demonstrates custom methods on cell renderers called by the application. The following can be noted:

• The medal columns are all using the user defined MedalCellRenderer. The cell renderer has an arbitrary method medalUserFunction() which prints some data to the console.
• The Gold method executes a method on all instances of the cell renderer in the gold column.
• The First Row Gold method executes a method on the gold cell of the first row only. Note that the getCellRendererInstances() method will return nothing if the grid is scrolled far past the first row showing row virtualisation in action.
• The All Cells method executes a method on all instances of all cell renderers.

Cell Renderer Keyboard Navigation

When using custom cell renderers, the custom cell renderer is responsible for implementing support for keyboard navigation among its focusable elements. This is why by default, focusing a grid cell with a custom cell renderer will focus the entire cell instead of any of the elements inside the custom cell renderer.

Adding support for keyboard navigation and focus requires a custom suppressKeyboardEvent function in grid options. See Suppress Keyboard Events.

An example of this is shown below, enabling keyboard navigation through the custom cell elements when pressing ⇥ Tab and ⇧ Shift+⇥ Tab:

• Click on the top left Natalie Coughlin cell, press the ⇥ Tab key and notice that the button, textbox and link can be tabbed into. At the end of the cell elements, the tab focus moves to the next cell in the next row
• Use ⇧ Shift+⇥ Tab to navigate in the reverse direction

The suppressKeyboardEvent callback is used to capture tab events and determine if the user is tabbing forward or backwards. It also suppresses the default behaviour of moving to the next cell if tabbing within the child elements.

If the focus is at the beginning or the end of the cell children and moving out of the cell, the keyboard event is not suppressed, so focus can move between the children elements. Also, when moving backwards, the focus needs to be manually set while preventing the default behaviour of the keyboard press event.