js兼容的placeholder属性详解

if (placeholder) {
    // 文本框ID
    var elementId = $element.attr('id');
    if (!elementId) {
        var now = new Date();
        elementId = 'lbl_placeholder' + now.getSeconds() + now.getMilliseconds();
        $element.attr('id', elementId);
    }

    // 添加label标签，用于显示placeholder的值
    var $label = $('<label>', {
        html: $element.val() ? '' : placeholder,
        'for': elementId,
        css:
            {
                position: 'absolute',
                cursor: 'text',
                color: '#a9a9a9',
                fontSize: $element.css('fontSize'),
                fontFamily: $element.css('fontFamily')
            }
    }).insertAfter($element);

    // 绑定事件
    var _setPosition = function () {
        $label.css({ marginTop: GetStringNumValue($element.css('marginTop')) + 8 + 'px', marginLeft: '-' + (GetStringNumValue($element.css('width')) - 6) + 'px' });
    }
    var _resetPlaceholder = function () {
        if ($element.val()) { $label.html(null); }
        else {
            _setPosition();
            $label.html(placeholder);
        }
    }
    _setPosition();
    $element.on('focus blur input keyup propertychange resetplaceholder', _resetPlaceholder);