JavaScript Callback after calling function

Ok so lets say I have this function:

function a(message) {
alert(message);
}

And I want to have a callback after the alert window is sh开发者_开发百科own. Something like this:

a("Hi.", function() {});

I'm not sure how to have a callback inside of the function I call like that.

(I'm just using the alert window as an example)

Thanks!

There's no special syntax for callbacks, just pass the callback function and call it inside your function.

function a(message, cb) {
    console.log(message); // log to the console of recent Browsers
    cb();
}

a("Hi.", function() {
    console.log("After hi...");
});

Output:

Hi.
After hi...

You can add a if statement to check whether you add a callback function or not. So you can use the function also without a callback.

function a(message, cb) {
    alert(message);
    if (typeof cb === "function") {
        cb();
    }
}

Here is the code that will alert first and then second. I hope this is what you asked.

function  basic(callback) {
    alert("first...");
    var a = "second...";
    callback(a);
} 

basic(function (abc) {
   alert(abc);
});