为什么我不能从输入框中获取文本值？

<input type="text" id="myInput">

// 正确的方式
var inputElement = document.getElementById('myInput');
var value = inputElement.value;

document.addEventListener('DOMContentLoaded', function() {
    var inputElement = document.getElementById('myInput');
    var value = inputElement.value;
});

var inputElement = document.getElementById('myInput');
if (inputElement.value) {
    console.log(inputElement.value);
} else {
    console.log('输入框为空');
}

try {
    var inputElement = document.getElementById('myInput');
    var value = inputElement.value;
} catch (e) {
    console.error(e);
}

<input type="text" id="myInput" disabled> <!-- 禁用状态 -->
<input type="text" id="myInput" style="display:none;"> <!-- 隐藏状态 -->

var inputElement = document.getElementById('myInput');
if (!inputElement.disabled && inputElement.style.display !== 'none') {
    var value = inputElement.value;
}