context2d.measureText returns incorrect value

Context2d.measureText says

The measureText() method returns an object that contains the width of the specified text, in pixels.

strokeRect also takes a width in pixels. This program creates a PDF with the text "hello world", and prints a rectangle below it according to its measured width

const jspdf = require("jspdf");
const fs = require("fs");

const doc = new jspdf.jsPDF({
    unit: "mm",
    format: [8.5 * 25.4, 11 * 25.4],
});

const ctx = doc.context2d;

doc.setFont("Helvetica");
doc.setFontSize(12);
doc.setFillColor(0, 0, 0);

const width = ctx.measureText("hello world");
ctx.fillText("hello world", 50, 50);

// Reported width
ctx.strokeRect(50, 55, width.width, 2);
// Correction attempt 1
ctx.strokeRect(50, 60, width.width / 2.8346456, 2);
// Correction attempt 2
ctx.strokeRect(50, 65, width.width / 2.8346456 * (96 / 72), 2);
// Correction attempt 3
ctx.strokeRect(50, 70, width.width / 2.8346456 * (72 / 96), 2);

fs.writeFile("test.pdf", Buffer.from(doc.output("arraybuffer")), () => {});

The top line, shown here, is not the same width as the text:

The next three lines show how to get from the returned value from the correct value; it looks like a lot of the math inside the implementation isn't necessary.

Additionally, the documented return type is Number, but it actually returns an object of the form { width: number } (as described in the general description).

https://github.com/MrRio/jsPDF/blob/cef97fb34eda41a8704c9f3983e680919a328ce4/src/modules/context2d.js#L1388

Start with src/modules/context2d.js around line 1388 and reproduce the issue using the JavaScript example in the report. Compare measureText’s returned width and documented return type with the rendered text and strokeRect output; done means the measurement and API documentation consistently match the expected text width and return shape.