我想添加一个验证来限制输入值，值必须小于5，如果它大于5，它应该显示错误

<input type="number" id="inputValue" min="0" max="5" onchange="validateInput()"/>
<div id="errorText" style="display: none; color: red;">输入值必须小于5</div>

<script>
function validateInput() {
    var input = document.getElementById("inputValue").value;
    var errorText = document.getElementById("errorText");

    if (input >= 5) {
        errorText.style.display = "block";
    } else {
        errorText.style.display = "none";
    }
}
</script>

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/validate", methods=["POST"])
def validate_input():
    input_value = int(request.form.get("inputValue"))

    if input_value >= 5:
        return jsonify(error="输入值必须小于5"), 400

    return jsonify(success=True)

if __name__ == "__main__":
    app.run()