Html，Placeholder，Jquery

先上图：

两种提示方式：

1,    placeholder,Jquery

<input class="loginInput" name="account" id="mobile" placeholder="手机号" type="text">

jQuery.fn.placeholder = function() {
    var i = document.createElement('input'),
        placeholdersupport = 'placeholder' in i;
    if (!placeholdersupport) {
        var inputs = jQuery(this);
        inputs.each(function() {
            var input = jQuery(this),
                text = input.attr('placeholder'),
                pdl = 0,
                height = input.outerHeight(),
                width = input.outerWidth(),
                placeholder = jQuery('<span class="phTips">' + text + '</span>');
            try {
                pdl = input.css('padding-left').match(/\d*/i)[0] * 1;
            } catch (e) {
                pdl = 5;
            }
            placeholder.css({
                'margin-left': -(width - pdl),
                'height': height,
                'line-height': height + "px",
                'position': 'absolute',
                'color': "#cecfc9",
                'font-size': "12px"
            });
            placeholder.click(function() {
                input.focus();
            });
            if (input.val() != "") {
                placeholder.css({
                    display: 'none'
                });
            } else {
                placeholder.css({
                    display: 'inline'
                });
            }
            placeholder.insertAfter(input);
            input.keyup(function(e) {
                if (jQuery(this).val() != "") {
                    placeholder.css({
                        display: 'none'
                    });
                } else {
                    placeholder.css({
                        display: 'inline'
                    });
                }
            });
        });
    }
    return this;
};
$(function() {
    jQuery('input[placeholder]').placeholder();
})

 2,    value,onblur

<input class="loginInput" name="account" id="mobile" value="手机号" type="text" 
onblur="if(this.value=='') this.value=this.defaultValue" 
onfocus="if (this.value==this.defaultValue) this.value = '';">

Tips:    具体使用哪种视情况而定。