TextFormatUpdateEvent

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The TextFormatUpdateEvent interface is a DOM event that represents a list of text formats that an Input Method Editor (IME) window wants to apply to the text being composed in an editable region that's attached to an EditContext instance.

This interface inherits properties from Event.

Event TextFormatUpdateEvent

Constructor

TextFormatUpdateEvent() Experimental

Creates a new TextFormatUpdateEvent object.

Instance methods

TextFormatUpdateEvent.getTextFormats Experimental

Returns an Array of TextFormat objects that represent the formats that the IME window wants to apply to the text.

Examples

Styling IME-composed text

In the following example, the textformatupdate event is used to update the formatting of the text in the editable region.

html
<canvas id="editor-canvas"></canvas>
js
const TEXT_X = 10;
const TEXT_Y = 10;

const canvas = document.getElementById("editor-canvas");
const ctx = canvas.getContext("2d");

const editContext = new EditContext();
canvas.editContext = editContext;

editContext.addEventListener("textformatupdate", (e) => {
  // Clear the canvas.
  ctx.clearRect(0, 0, canvas.width, canvas.height);

  // Render the text.
  ctx.fillText(editContext.text, TEXT_X, TEXT_Y);
  console.log(`Rendering text: ${editContext.text}`);

  // Get the text formats that the IME window wants to apply.
  const formats = e.getTextFormats();

  // Iterate over the text formats
  for (const format of formats) {
    const { rangeStart, rangeEnd, underlineStyle, underlineThickness } = format;

    console.log(
      `Applying underline ${underlineThickness} ${underlineStyle} between ${rangeStart} and ${rangeEnd}.`,
    );

    const underlineXStart = ctx.measureText(
      editContext.text.substring(0, rangeStart),
    ).width;
    const underlineXEnd = ctx.measureText(
      editContext.text.substring(0, rangeEnd),
    ).width;
    const underlineY = TEXT_Y + 3;

    // For brevity, this example only draws a simple underline.
    // Use underlineStyle and underlineThickness to draw the correct underline.

    ctx.beginPath();
    ctx.moveTo(TEXT_X + underlineXStart, underlineY);
    ctx.lineTo(TEXT_X + underlineXEnd, underlineY);
    ctx.stroke();
  }
});

Specifications

Specification
EditContext API
# dom-textformatupdateevent

Browser compatibility

BCD tables only load in the browser