Return value of coherent echo

The return value of echo. The return value of echo is verified by ajax. It is found that when PHPcodeecho & quot; a & quot;, the client alert finds that it is an array with a length of 5. the first three are empty and the first 4th are, the last one is undefined. PHPcodeecho1; the return value of echo.
The return value of echo is verified by ajax.
When

PHP code

  Echo "";

The client alert finds that it is an array of 5 characters, the first three are empty, the first 4th are a, and the last is undefined.

PHP code

  Echo 1;

When the client alert, it is found to be a 4-length array, the first three are empty, and the first 4th are 1.

You must remove spaces before matching... What is the situation?


------ Solution --------------------
The PHP file is saved as a UTF-8 without BOM format.