Oko*_*000 5

首先,你应该使用MooTools的插件"OverText" http://mootools.net/docs/more/Forms/OverText基本上模拟了这种功能.它实际上可以在任何浏览器中工作,因此,如果您愿意,可以使用它并完全忘记占位符属性.但是,如果您希望在可用时支持占位符,但是对于旧版浏览器使用OverText,则可以这样做:

window.addEvent('domready', function() {
    // create a test element
    var test = new Element('input'); 
    // if it has 'placeholder' this browser supports it already so you can exit
    if(("placeholder" in test)) { return; } 
    // for older browsers, get all the inputs which you have assigned a 'placeholder' attribute to
    $$('input[placeholder]').each(function(el) { 
        // and create an overtext for them using the value of the placeholder attribute
        new OverText(el, { textOverride: el.get('placeholder') });
    });
});
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