how to change <meter> values?

问题

I'm a beginner at HTML, and while learning about HTML5 I've found a cool tool, the <meter>. However, it won't update; it's there as a static value!

My question is simple: how do I use the length of a <textarea> to change the color of <meter>, so that the user will, for example, see red when he reaches 160 characters (the maximum value)? In other words, count the <textarea> characters, and send them to the value of the meter tag.

回答1:

Note that not all browser will support this tag. E.g. no support by IE until IE10. http://caniuse.com/#search=meter.

Something like this should work:

HTML

<textarea id="sometext"></textarea>
<meter value="10" min="0" max="160" id="somemeter">2 out of 160</meter>​

JS

(function() {
    var textarea = document.getElementById('sometext');
    var meter = document.getElementById('somemeter');

    var theLength = 0;

    textarea.addEventListener('keypress', function() {
        theLength = textarea.value.length;

        if (theLength > 160) {
            theLength = 160;
        }

        meter.value = theLength;
    });
})();​

Demo: http://jsfiddle.net/RBUmQ/1/

回答2:

if you use jquery

$("#meter_id").val($("my_text_area_id").val().length)

at least i think .... something like that anyway

回答3:

What you need to do is write a function which counts the length of text in the textarea and sets the value of meter to that count.

Then, you need to add a listener to the textarea. Whether it's a keyup or a keypress or whatever you decide to use.

When that event happens, fire your function.

回答4:

i've combined the both (inspired from them), and it worked :) , handles copy, past, and updates in real time :)

javascript:

var meter = document.getElementById('shower');

function textCounter(field,maxlimit) {
field.value = field.value.substring(0, maxlimit);
var theLength = field.value.length;
meter.value = theLength;
}

html

<textarea name="description" id="description" rows="3" cols="60" required title="vous  devez mettre une petite description" placeholder="escence, 2006, roulant 100000km, toutes  options, siege en cuir" onKeyDown="textCounter(document.formacha.description,160)" onKeyUp="textCounter(document.formacha.description, 160)"></textarea>
<meter name="shower" min="1" max="160" value="1"id="shower" low="30" high="140">afficher son etat</meter>

来源：https://stackoverflow.com/questions/12168992/how-to-change-meter-values