如何在文本区域内映射键TAB

<textarea id="myTextarea"></textarea>

<script>
    var textarea = document.getElementById("myTextarea");
    textarea.addEventListener("keydown", function(event) {
        if (event.key === "Tab") {
            event.preventDefault();
            var start = this.selectionStart;
            var end = this.selectionEnd;
            var value = this.value;
            this.value = value.substring(0, start) + "\t" + value.substring(end);
            this.selectionStart = this.selectionEnd = start + 1;
        }
    });
</script>