在自定义工具函数中，遇到js中的call的一个问题

hellostarfish 2017-01-17 11:20:08

下面代码中的$.formatDate.patternValue[matched[0]].call(this,date)这一句call应该怎么理解啊？

(function($){
$.formatDate=function(date,pattern){
var result=[];
while(pattern.length>0){
$.formatDate.patternParts.lastIndex=0;
var matched=$.formatDate.patternParts.exec(pattern);
if(matched){
console.log(this);
console.log(matched[0]);
console.log($.formatDate.patternValue[matched[0]]);
result.push(
$.formatDate.patternValue[matched[0]].call(this,date)
);
pattern=pattern.slice(matched[0].length);
}else{
result.push(pattern.charAt(0));
pattern=pattern.slice(1);
}

}
return result.join('/');
};

$.formatDate.patternParts=/^(yy(yy)?|M(M(M(M)?)?)?|d(d)?|EEE(E)?|a|H(H)?|h(h)?|m(m)?|s(s)?|S)/;
$.formatDate.monthNames=['January','February','March','April','May','June','July',
'August','September','October','November','December'];
$.formatDate.dayNames=['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday', 'Saturday'];

$.formatDate.patternValue={
yy:function(date){
return $.toFixedWidth(date.getFullYear(),2);
},
yyyy:function(date){
return date.getFullYear().toString();
},
MMMM:function(date){
return $.formatDate.monthNames[date.getMonth()];
},
MMM:function(date){
return $.formatDate.monthNames[date.getMonth()].substr(0,3);
},
MM:function(date){
return $.toFixedWidth(date.getMonth()+1,2);
},
M:function(date){
return date.getMonth()+1;
},
dd:function(date){
return $.toFixedWidth(date.getDate(),2);
},
d:function(date){
return date.getDate();
},
EEEE:function(date){
return $.formatDate.dayNames[date.getDay()];
},
EEE:function(date){
return $.formatDate.dayNames[date.getDay()].substr(0,3);
},
HH:function(date){
return $.toFixedWidth(date.getHours(),2);
},
H:function(date){
return date.getHours();
},
hh:function(date){
var hours=date.getHours();
return $.toFixedWidth(hours>12?hours-12:hours,2);
},
h:function(date){
return date.getHours()%12;
},
mm:function(date){
return $.toFixedWidth(date.getMinutes(),2);
},
m:function(date){
return date.getMinutes();
},
ss:function(date){
return $.toFixedWidth(date.getSeconds(),2);
},
s:function(date){
return date.getSeconds();
},
S:function(date){
return $.toFixedWidth(date.getMilliseconds(),3);
},
a:function(date){
return date.getHours()<12?'AM':'PM';
}

}

})(jQuery);