由于placeholder是個(gè)新增屬性，目前只有少數(shù)瀏覽器支持，如何檢測(cè)瀏覽器是否支持它呢？(更多HTML5/CSS3特性檢測(cè)可以訪問(wèn))

function hasPlaceholderSupport() {
  return 'placeholder' in document.createElement('input');
}

默認(rèn)提示文字是灰色的，可以通過(guò)CSS來(lái)改變文字樣式：

/* all */
::-webkit-input-placeholder { color:#f00; }
input:-moz-placeholder { color:#f00; }
 
/* individual: webkit */
#field2::-webkit-input-placeholder { color:#00f; }
#field3::-webkit-input-placeholder { color:#090; background:lightgreen; text-transform:uppercase; }
#field4::-webkit-input-placeholder { font-style:italic; text-decoration:overline; letter-spacing:3px; color:#999; }
 
/* individual: mozilla */
#field2:-moz-placeholder { color:#00f; }
#field3:-moz-placeholder { color:#090; background:lightgreen; text-transform:uppercase; }
#field4:-moz-placeholder { font-style:italic; text-decoration:overline; letter-spacing:3px; color:#999; }

兼容其他不支持placeholder的瀏覽器：

var PlaceHolder = {
    _support: (function() {
        return 'placeholder' in document.createElement('input');
    })(),

    //提示文字的樣式，需要在頁(yè)面中其他位置定義
    className: 'abc',

    init: function() {
        if (!PlaceHolder._support) {
            //未對(duì)textarea處理，需要的自己加上
            var inputs = document.getElementsByTagName('input');
            PlaceHolder.create(inputs);
        }
    },

    create: function(inputs) {
        var input;
        if (!inputs.length) {
            inputs = [inputs];
        }
        for (var i = 0, length = inputs.length; i <length; i++) {
            input = inputs[i];
            if (!PlaceHolder._support && input.attributes && input.attributes.placeholder) {
                PlaceHolder._setValue(input);
                input.addEventListener('focus', function(e) {
                    if (this.value === this.attributes.placeholder.nodeValue) {
                        this.value = '';
                        this.className = '';
                    }
                }, false);
                input.addEventListener('blur', function(e) {
                    if (this.value === '') {
                        PlaceHolder._setValue(this);
                    }
                }, false);
            }
        }
    },

    _setValue: function(input) {
        input.value = input.attributes.placeholder.nodeValue;
        input.className = PlaceHolder.className;
    }
};

//頁(yè)面初始化時(shí)對(duì)所有input做初始化
//PlaceHolder.init();
//或者單獨(dú)設(shè)置某個(gè)元素
//PlaceHolder.create(document.getElementById('t1'));