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<!DOCTYPE html> <html> <body> <h2>JavaScript For In</h2> <p>for in 语句可以遍历数组值：</p> <p id="demo"></p> <script> const numbers = [45, 4, 9, 16, 25]; let txt = ""; for (let x in numbers) { txt += numbers[x] + "<br>"; } document.getElementById("demo").innerHTML = txt; </script> </body> </html>