How to Accurately Calculate Text Width in JavaScript Without Monospace Fonts?

Calculating Text Width in JavaScript Without Monospace Typeface

Question:

How can text width be accurately calculated in JavaScript without relying on monospace fonts?

Answer:

In HTML 5, the Canvas.measureText method provides a solution. Here's an example:

function getTextWidth(text, font) {
  const canvas = document.createElement('canvas');
  const context = canvas.getContext('2d');
  context.font = font;
  const metrics = context.measureText(text);
  return metrics.width;
}

This function measures text width in pixels based on a specified font. For instance:

console.log(getTextWidth('hello there!', 'bold 12pt arial')); // Outputs approximately 86

You can also determine font settings from existing elements using the getCanvasFont utility function:

function getCanvasFont(el) {
  const fontWeight = getCssStyle(el, 'font-weight') || 'normal';
  const fontSize = getCssStyle(el, 'font-size') || '16px';
  const fontFamily = getCssStyle(el, 'font-family') || 'Times New Roman';
  return `${fontWeight} ${fontSize} ${fontFamily}`;
}

const fontSize = getTextWidth(text, getCanvasFont(myEl));

Advantages and Considerations

This approach offers advantages over DOM-based methods:

• Conciseness and safety
• Customization options (e.g., textAlign, textBaseline)

However, note that:

• Padding, margin, and border need to be accounted for when adding text to the DOM
• Different browsers may provide sub-pixel or integer accuracy
• Firefox exhibits faster performance with Canvas method

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