现场演示

<input id="my_input" style="width: 400px; height: 30px;" value="some text to select">
<br>
<button id="select-bn" style="width: 100px; height: 30px; margin-top: 20px;cursor:pointer;">Select all</button>
<br><br>
OR 
<br><br>
Click to copy
<br><br>
<input id="my_input_copy" style="width: 400px; height: 30px;" value="some text to select and copy">
<br>
<button id="select-bn-copy" style="width: 170px; height: 30px; margin-top: 20px;cursor:pointer;">Click copy text</button>


<script type="text/javascript">
$(document).on('click', '#select-bn', function() {
  $("#my_input").select();
});


//click to select and copy to clipboard

var text_copy_bn = document.getElementById("select-bn-copy");
text_copy_bn.addEventListener('click', function(event) {
  var copy_text = document.getElementById("my_input_copy");
  copy_text.focus();
  copy_text.select();
  try {
    var works = document.execCommand('copy');
    var msg = works ? 'Text copied!' : 'Could not copy!';
    alert(msg);
  } catch (err) {
    alert('Sorry, could not copy');
  }
});
</script>

捕获单击事件的问题是，文本中的每次后续单击都将再次选择它，而用户可能希望重新定位光标。

对我有用的是声明一个变量selectSearchTextOnClick，并在默认情况下将其设置为true。点击处理程序检查变量是否仍然为true:如果为true，则将其设置为false并执行select()。然后我有一个模糊事件处理程序，将其设置为true。

到目前为止，结果似乎是我所期望的。

(编辑:我忘了说我曾尝试按照某人的建议捕获焦点事件，但这不起作用:焦点事件触发后，点击事件可以触发，立即取消选择文本)。

我在vue应用程序中使用焦点属性

<input @focus="$event.target.select()" />

在输入字段中使用“占位符”而不是“值”。

Html(你必须把onclick属性放在你想要它在页面上工作的每个输入上)

 <input type="text" value="click the input to select" onclick="this.select();"/>

或者一个更好的选择

jQuery(这将适用于页面上的每个文本输入，不需要改变你的html):

<script  type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.js"></script>  
<script type="text/javascript">
    $(function(){
        $(document).on('click','input[type=text]',function(){ this.select(); });
    });
</script>

If you are just trying to have placeholder text that gets replaced when a user selects the element then it is obviously best practice to use placeholder attribute nowadays. However, if you want to select all of the current value when a field gains focus then a combination of @Cory House and @Toastrackenigma answers seems to be most canonical. Use focus and focusout events, with handlers that set/release the current focus element, and select all when focused. An angular2/typescript example is as follows (but would be trivial to convert to vanilla js):

模板:

<input type="text" (focus)="focus()" (focusout)="focusout()" ... >

组件:

private focused = false;

public focusout = (): void => {
    this.focused = false;
};

public focus = (): void => {
    if(this.focused) return;
    this.focused = true;

    // Timeout for cross browser compatibility (Chrome)
    setTimeout(() => { document.execCommand('selectall', null, false); });
};