style="width: ___" vs width="___"

There are two ways to define the dimension for an element:
  • Using the height or width attributes:
    <img height="100" />
  • Or using the height or width property in CSS styles:
    <img style="height: 100px" />

Differences

  1. The width and height properties are available for all HTML elements. But the width and height attributes are only available for some elements such as canvas, image, table, td, etc.
    <!-- Work -->
    <img width="200px" />
    
    <!-- Does NOT work -->
    <div width="200px">
  2. For canvas elements, they don't produce the same result.
    According to the HTML specifications, if the width and height attributes are missing then the default value will be used.
    The width attribute defaults to 300, and the height attribute defaults to 150.
    It's recommended to set the height and width attributes for canvas directly or via JavaScript to avoid the problem that the canvas is stretched.
    <!-- Work -->
    <canvas height="100" width="100">
    
    <!-- Does NOT work -->
    <canvas style="height: 100px; width: 100px;">
    The width and height attributes of canvas must be positive numbers without the units. width="100px" will have no affect despite the fact that it seems to be a valid attribute declaration for other elements.
  3. The CSS style properties have the higher priority than the HTML properties.
    In the following example, the height: 200px property will override the height="100px" attribute:
    <!-- The image will have the width of 200px -->
    <img height="100px" style="height: 200px" />

Good to know

The width and height attributes are still used widely in emails where we have to support multiple screen sizes (mobile, desktop) and various email clients.
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