js获取textbox 的值

<input type="text" id="myTextbox">
<button onclick="getTextValue()">获取值</button>

<script>
function getTextValue() {
    var value = document.getElementById("myTextbox").value;
    console.log(value);
}
</script>

<input type="text" name="myTextbox">
<button onclick="getTextValue()">获取值</button>

<script>
function getTextValue() {
    var textbox = document.getElementsByName("myTextbox")[0];
    var value = textbox.value;
    console.log(value);
}
</script>

<input type="text" class="myTextbox">
<button onclick="getTextValue()">获取值</button>

<script>
function getTextValue() {
    var textbox = document.getElementsByClassName("myTextbox")[0];
    var value = textbox.value;
    console.log(value);
}
</script>

<input type="text" class="myTextbox">
<button onclick="getTextValue()">获取值</button>

<script>
function getTextValue() {
    var textboxes = document.getElementsByTagName("input");
    for (var i = 0; i < textboxes.length; i++) {
        if (textboxes[i].classList.contains("myTextbox")) {
            console.log(textboxes[i].value);
            break;
        }
    }
}
</script>