how can you figure out the week from a single date

I am building a project and in that project the user is going to input a 开发者_开发问答date eg. 8/2/2011. then i am going to show them the information for the week that contains 8/2/2011. How can you figure out which week to show? for this project i am using javascript, jquery, and php.

You should be able to do what you want by getting the first day of the week the given date occurs in.

If your weeks start on Monday:

Date.prototype.lastMonday=function(){
    var d= new Date(this), weekstart= 1;    
    while(d.getDay()!== 1) d.setDate(d.getDate()-1)
    return d;
}

alert(new Date().lastMonday())

//returns the current date if does fall on a Monday

If you want to know the days that compose the week you can just find out the day of the week and show the appropriate days before and after. To know the day of the week just use the getDay method of the Date object(see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getDay). For more info on the Date object see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date.