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• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

只读 emHeightAscent 特性为 TextMetrics 接口是 double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the top of the em square in the line box, in CSS pixels.

范例

const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
const text = ctx.measureText('foo'); // returns TextMetrics object
text.emHeightAscent; // 7.59765625;
					

规范

规范
HTML 实时标准 The definition of 'TextMetrics.emHeightAscent' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
emHeightAscent	Chrome Yes Disabled Yes Disabled Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.	Edge 79 Disabled 79 Disabled Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.	Firefox 74	IE No	Opera ?	Safari Yes	WebView Android No	Chrome Android Yes Disabled Yes Disabled Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No	Opera Android ?	Safari iOS Yes	Samsung Internet Android No

图例

完整支持

完整支持

不支持

不支持

兼容性未知 ?

兼容性未知

实验。期望将来行为有所改变。

实验。期望将来行为有所改变。

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

• TextMetrics

元数据

• 最后修改： Feb 26, 2020

相关话题

1. 画布 API
2. TextMetrics
3. 特性

   1. actualBoundingBoxAscent
   2. actualBoundingBoxDescent
   3. actualBoundingBoxLeft
   4. actualBoundingBoxRight
   5. alphabeticBaseline
   6. emHeightAscent
   7. emHeightDescent
   8. fontBoundingBoxAscent
   9. fontBoundingBoxDescent
   10. hangingBaseline
   11. ideographicBaseline
   12. width
4. Related pages for Canvas API

   1. Canvas
   2. CanvasGradient
   3. CanvasImageSource
   4. CanvasPattern
   5. CanvasRenderingContext2D
   6. HTMLCanvasElement
   7. ImageBitmap
   8. ImageBitmapFactories
   9. ImageBitmapRenderingContext
   10. ImageData
   11. OffscreenCanvas
   12. Path2D
   13. RenderingContext