How do I add a default text to the beginning of an

问题:

Im building a personal little social network. As part of the design, all statuses should begin with a default text that shouldn't change, similar to "Hi, my name is…" and then the user finishes the rest. Kind of like an HTML5 placeholder that doesn't go away. What would be the best way to accomplish this?

回答1:

Note: For some dumb reason, I assumed jQuery (note that you do not need jQuery for this, but makes it a little easier).

Here is one solution uses a combination of text-indent and an absolutely positioned <span> (for the prefix part).

Demo: http://jsfiddle.net/4YzZy/

---

$('textarea.withprefix').each(function() {
  var prefix = $('<span/>')
              .text($(this).data('prefix'))
              .addClass('prefix')
              .appendTo('body')
              .css({
                  left: $(this).position().left + 'px',
                  top: $(this).position().top + 'px',
              });
  $(this).css({textIndent: prefix.outerWidth() + 'px'});
});

textarea, span.prefix {
    font-family: arial; /* change these as needed, but ensure that the textarea and the span use the same font */
    font-size: 1em;
    font-weight: normal;
    padding: 2px;
    border-width: 1px;
}
span.prefix {
    position:absolute;   
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<textarea class="withprefix" data-prefix="Hi There, "></textarea>

回答2:

Please refer this fiddle If it serves the purpose, then please find the code below.

Markup:

<textarea id='status'>
Hi, my name is...
</textarea>

JavaScript:

document.querySelector('#status').addEventListener('input', function(e){
    var defaultText = 'Hi, my name is...',
        defaultTextLength = defaultText.length;
    if(this.selectionStart === this.selectionEnd && this.selectionStart defaultTextLength {
        this.value = defaultText;
    }
});

回答3:

If you want to use javascript to perform your task, you can set up some event listeners and then when the user makes a change, check to see if that change affected the text you want changed. Sarbbottam's new code does this, but it will replace any text you have already typed if you modify the original text. I have fixed this by saving the previous value of the textarea.

HTML:

<textarea id="text">Hello, my name is </textarea>

Javascript:

var defaultText = "Hello, my name is ";
var valueOnKeyDown = new Array();
document.getElementById("text").addEventListener("keydown", function() {
    valueOnKeyDown.push(this.value);
}, false);
document.getElementById("text").addEventListener("keyup", function(e) {
    if(valueOnKeyDown[0].substring(0, defaultText.length) != this.value.substring(0, defaultText.length)) {
        this.value = valueOnKeyDown[0];
    }
    valueOnKeyDown = new Array();
}, false);

And of course a working demo.

Another option that may work that is not mentioned in the other answers is to set up a keydown/keypress event listener and get the caret position in the textarea using javascript. If it is less than the length of your default text, you just call event.preventDefault(). The main disadvantage to this is that it may not be possible to make this completely cross-browser compatible.

回答4:

If the goal is that the user cannot change this text then you can do a couple of things:

1. add the text outside of the textarea (above it for instance)
2. Add the text outside of the textarea but place it behind the textarea using css. You can make the textarea transparent so the user can see the text. The problem there would be that the text the user types can fall over the text you placed in the background
3. Put it in a background image of the textarea
4. Place the text inside the textarea (<textarea>Hi, my name is </textarea>) and use JavaScript to test for what has been typed and change the text if it changes into something that you do not want. There are masking plugins that you can use to do this.

The best options would be the first option and the forth. I'd go the first as it is by far the easiest