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HTMLImageElement.y - Web APIs 编辑

The read-only HTMLImageElement property y indicates the y-coordinate of the <img> element's top border edge relative to the root element's origin.

The x and y properties are only valid for an image if its display property has the computed value table-column or table-column-group. In other words: it has either of those values set explicitly on it, or it has inherited it from a containing element, or by being located within a column described by either <col> or <colgroup>.

Syntax

let imageY = htmlImageElement.y;

Value

An integer value indicating the distance in pixels from the top edge of the element's nearest root element to the top edge of the <img> element's border box. The nearest root element is the outermost <html> element that contains the image. If the image is in an <iframe>, its y is relative to that frame.

In the diagram below, the top border edge is the top edge of the blue padding area. So the value returned by y would be the distance from that point to the top edge of the content area.

Diagram showing the relationships between the various boxes associated with an element

Note: The y property is only valid if the computed value of the image's display property is either table-column or table-column-group; in other words, either of those are set directly on the <img> or they're inherited from a containing element or by being located within a column described by either <col> or <colgroup>.

Example

The example below demonstrates the use of the HTMLImageElement properties x and y.

HTML

In this example, we see a table showing information about users of a web site, including their user ID, their full name, and their avatar image.

<table id="userinfo">
  <colgroup>
    <col span="2" class="group1">
    <col>
  </colgroup>
  <tr>
    <th>UserID</th>
    <th>Name</th>
    <th>Avatar</th>
  </tr>
  <tr>
    <td>12345678</td>
    <td>Johnny Rocket</td>
    <td><img src="https://interactive-examples.mdn.mozilla.net/media/examples/grapefruit-slice-332-332.jpg"</td>
  </th>
</table>
<pre id="log">
</pre>

JavaScript

The JavaScript code that fetches the image from the table and looks up its x and y values is below.

let logBox = document.querySelector("pre");
let tbl = document.getElementById("userinfo")

let log = msg => {
  logBox.innerHTML += `${msg}<br>`;
}

let cell = tbl.rows[1].cells[2];
let image = cell.querySelector("img");

log(`Image's global X: ${image.x}`);
log(`Image's global Y: ${image.y}`);

This uses the <table>'s rows property to get a list of the rows in the table, from which it looks up row 1 (which, being a zero-based index, means the second row from the top). Then it looks at that <tr> (table row) element's cells property to get a list of the cells in that row. The third cell is taken from that row (once again, specifying 2 as the zero-based offset).

From there, we can get the <img> element itself from the cell by calling querySelector() on the HTMLTableCellElement representing that cell.

Finally, we can look up and display the values of the HTMLImageElement's x and y properties.

CSS

The CSS defining the appearance of the table:

.group1 {
  background-color: #d7d9f2;
}

table {
  border-collapse: collapse;
  border: 2px solid rgb(100, 100, 100);
  font-family: sans-serif;
}

td, th {
  border: 1px solid rgb(100, 100, 100);
  padding: 10px 14px;
}

td > img {
  max-width: 4em;
}