What should I do if the js output by PHP is not executed?

The js output by PHP is not executed

<?php
    echo "<script>alert(&#39;我弹出来了&#39;)</script>";
?>

You can output the JS script in PHP to the browser in one sentence implement. (Recommendation: "PHP Tutorial")

But today I encountered a very strange problem, that is, this code just outputs a string under Chrom and Firefox, and is not executed. An alert pops up.

Principle:

MIME chrome does not parse text/plain. PHP can use header to output html, and the browser uses the last output header as content-type

header('Content-Type:text/html;charset=utf-8');

text/plain html will not be executed.

Just need to re-header before alert.

if(!uploadFile())
{
    echo "<script>alert(&#39;上传文件失败&#39;)</script>";    
}
header(&#39;Content-Type:text/html;charset=utf-8&#39;);
echo ("")

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