javascript - change time string of HH:mm am/pm to 24 hour time

Question

I get a variable string like so:

8:45 am

And want, if it is pm, to convert it to 24 hour time. So that I can then drop the am/pm and use it with something else.

I can drop the am/pm quite easily like this:

function replaceEnds(string) {
        string = string.replace("am", "");
        string = string.replace("pm", "");
        return string;
    }

But of course if I do that, I don't know if the string is am or pm, so I don't know to add 12 hours on to the string to make it 24 hour.

Anyone know how I could resolve this? I absolutely cannot change the input that I get of the variable, it'll always be the hour (in 12 hour time), minutes, and am or pm.

Answer 1

Without using any additional JavaScript libraries:

/**
 * @var amPmString - Time component (e.g. "8:45 PM")
 * @returns - 24 hour time string
 */
function getTwentyFourHourTime(amPmString) { 
    var d = new Date("1/1/2013 " + amPmString); 
    return d.getHours() + ':' + d.getMinutes(); 
}

So for example:

getTwentyFourHourTime("8:45 PM"); // "20:45"
getTwentyFourHourTime("8:45 AM"); // "8:45"