如何在textarea中添加更多文本

I want to create console.

I have textarea:

<textarea style="width: 100%; height: 300px; resize: none;" id="console_output" readonly></textarea>

And using this code to insert more text:

else echo "<script>$('#console_output').append('Some text.
');</script>";

But nothing happened, textarea is empty.

Your code should work as you can check JsFiddle

$('#console_output').append('Some text.
');

Will not work if

1. you are not into your else statement
2. textarea is not there yet if dynamically created
3. you have no jquery included

You can try with pure js:

echo '<script>document.getElementById("console_output").value += "Some text.
";</script>';