当element是表单的一部分时，document.getElementById返回null

Question

I have php file that has some javascript inside. Consider the following javascript code, which prints null to the console (line 124 in the file):

console.log(document.getElementById('d_min')); 

Below the script, I have the following form (line 140 in the file):

<FORM name="DataCollect" ACTION="save_phase1.php" method="post">
    <input type="hidden" name="d_min" id="d_min" value=""/>
</FORM>

Why is it that it could be null? Why can't it find that element?

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I FIXED THE PROBLEM:

I put the entire <form> as a document.write statement after the existing document.write statements I had.

Answer 1

The DOM is not fully loaded by the time the script executes. Move your script below that form and see if you get better results.