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The TextMetrics interface represents the dimensions of a piece of text in the canvas; a textMetrics() instance can be retrieved using the CanvasRenderingContext2D.measureText() method.

Properties

TextMetrics.width Read only
Is a double giving the calculated width of a segment of inline text in CSS pixels. It takes into account the current font of the context.
TextMetrics.actualBoundingBoxLeft Read only
Is a double giving the distance from the alignment point given by the CanvasRenderingContext2D.textAlign property to the left side of the bounding rectangle of the given text, in CSS pixels. The distance is measured parallel to the baseline.
TextMetrics.actualBoundingBoxRight Read only
Is a double giving the distance from the alignment point given by the CanvasRenderingContext2D.textAlign property to the right side of the bounding rectangle of the given text, in CSS pixels. The distance is measured parallel to the baseline.
TextMetrics.fontBoundingBoxAscent Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the top of the highest bounding rectangle of all the fonts used to render the text, in CSS pixels.
TextMetrics.fontBoundingBoxDescent Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle of all the fonts used to render the text, in CSS pixels.
TextMetrics.actualBoundingBoxAscent Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the top of the bounding rectangle used to render the text, in CSS pixels.
TextMetrics.actualBoundingBoxDescent Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle used to render the text, in CSS pixels.
TextMetrics.emHeightAscent Read only
Is a 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.
TextMetrics.emHeightDescent Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the bottom of the em square in the line box, in CSS pixels.
TextMetrics.hangingBaseline Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the hanging baseline of the line box, in CSS pixels.
TextMetrics.alphabeticBaseline Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the alphabetic baseline of the line box, in CSS pixels.
TextMetrics.ideographicBaseline Read only
Is a double giving the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the ideographic baseline of the line box, in CSS pixels.

Examples

Baselines illustrated

This example demonstrates the baselines the TextMetrics object holds. The default baseline is the alphabeticBaseline. See also the CanvasRenderingContext2D.textBaseline property.

HTML

<canvas id="canvas" width="550" height="500"></canvas>

JavaScript

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

const baselinesAboveAlphabetic = ['fontBoundingBoxAscent', 'actualBoundingBoxAscent', 
                   'emHeightAscent', 'hangingBaseline'];
const baselinesBelowAlphabetic = ['ideographicBaseline', 'emHeightDescent', 
                   'actualBoundingBoxDescent', 'fontBoundingBoxDescent'];
const baselines = [...baselinesAboveAlphabetic, ...baselinesBelowAlphabetic];
ctx.font = '25px serif';
ctx.strokeStyle = 'red';

baselines.forEach(function (baseline, index) {
  let text = 'Abcdefghijklmnop (' + baseline + ')';
  let textMetrics = ctx.measureText(text);
  let y = 50 + index * 50;
  ctx.beginPath();
  ctx.fillText(text, 0, y);
  let lineY = y - Math.abs(textMetrics[baseline]);
  if (baselinesBelowAlphabetic.includes(baseline)) {
    lineY = y + Math.abs(textMetrics[baseline]);
  }
  ctx.moveTo(0, lineY);
  ctx.lineTo(550, lineY);
  ctx.stroke();
  
});

Result

Measuring text width

When measuring the x-direction of a piece of text, the sum of actualBoundingBoxLeft and actualBoundingBoxRight can be wider than the width of the inline box (width), due to slanted/italic fonts where characters overhang their advance width.

It can therefore be useful to use the sum of actualBoundingBoxLeft and actualBoundingBoxRight as a more accurate way to get the absolute text width:

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
const text = 'Abcdefghijklmnop';
ctx.font = 'italic 50px serif';
const textMetrics = ctx.measureText(text);

console.log(textMetrics.width);
// 459.8833312988281

console.log(Math.abs(textMetrics.actualBoundingBoxLeft) +
            Math.abs(textMetrics.actualBoundingBoxRight));
// 462.8833333333333

Specifications

Specification
HTML Living Standard
The definition of 'TextMetrics' in that specification.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
TextMetricsChrome Full support 4Edge Full support 12Firefox Full support 1.5IE Full support 9Opera Full support 9Safari Full support 3.1WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 31Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes
actualBoundingBoxAscent
Experimental
Chrome Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79Firefox Full support 74IE No support NoOpera ? Safari Full support YesWebView Android Full support 77Chrome Android Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android Full support 12.0
actualBoundingBoxDescent
Experimental
Chrome Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79Firefox Full support 74IE No support NoOpera ? Safari Full support YesWebView Android Full support 77Chrome Android Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android Full support 12.0
actualBoundingBoxLeft
Experimental
Chrome Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79Firefox Full support 74IE No support NoOpera ? Safari Full support YesWebView Android Full support 77Chrome Android Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android Full support 12.0
actualBoundingBoxRight
Experimental
Chrome Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79Firefox Full support 74IE No support NoOpera ? Safari Full support YesWebView Android Full support 77Chrome Android Full support 77
Full support 77
No support ? — 77
Disabled
Disabled Until version 77 (exclusive): this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android Full support 12.0
alphabeticBaseline
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.baselines.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
emHeightAscent
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.emHeight.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
emHeightDescent
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.emHeight.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
fontBoundingBoxAscent
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.fontBoundingBox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
fontBoundingBoxDescent
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.fontBoundingBox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS No support NoSamsung Internet Android No support No
hangingBaseline
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.baselines.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
ideographicBaseline
Experimental
Chrome Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 79
Disabled
Full support 79
Disabled
Disabled From version 79: this feature is behind the Experimental Web Platform Features preference.
Firefox Full support 74
Disabled
Full support 74
Disabled
Disabled From version 74: this feature is behind the dom.textMetrics.baselines.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera ? Safari Full support YesWebView Android No support NoChrome Android Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Firefox Android No support NoOpera Android ? Safari iOS Full support YesSamsung Internet Android No support No
width
Experimental
Chrome Full support 4Edge Full support 12Firefox Full support 1.5IE Full support 9Opera Full support 9Safari Full support 3.1WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 31Opera Android Full support YesSafari iOS Full support 3.2Samsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

文件標籤與貢獻者

最近更新: chrisdavidmills,