The CanvasRenderingContext2D.measureText() method returns a TextMetrics object that contains information about the measured text (such as its width, for example).
measureText(text)textThe text string to measure.
A TextMetrics object.
Given this <canvas> element:
<canvas id="canvas"></canvas>… you can get a TextMetrics object using the following code:
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
let text = ctx.measureText("Hello world");
console.log(text.width); // 56;CanvasRenderingContext2DTextMetrics