HTML输入中不可更改的前导字符? [英] unchangeable leading characters in HTML input?

问题描述

如何生成一个输入元素，该输入元素的默认起始值​​不可更改?例如，我正在从用户那里寻找一个数字，但是我希望"333"已经存在于输入文本框中，因为所有输入都将从该数字开始.我也不希望用户能够更改它.我还需要将333用作值的一部分，而不仅仅是通过样式添加，因为我需要对其进行验证.

How do I generate an input element that has a default starting value in there that is unchangeable? For example, I am looking for a number from the user but I want '333' to be already in the input text box since all inputs will start with that number. I also don't want the user to be able to change it. I need the 333 to be part of the value also rather than just being added via style since I need to do validation on it.

推荐答案

使用JavaScript的一种可能性:

One possibilty using JavaScript:

nine = document.getElementById("nine");
nine.addEventListener("keydown", function (ev) {
  var el = this;
  var value = el.value;
  setTimeout(function () {
    if (el.value.indexOf("333") != 0) {
      el.value = value;
    } 
  }, 0);
});

<input type="text" value="333" id="nine" />

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