I have code like this about five times in my project, and I know I'm going to have it more often than that:

this.messageHandler = ({ data, origin }) => {
    if (origin === window.location.origin) {
        if (
            data.listener === this.listener &&
            data.event === 'rowclick'
        ) {
            this.recordId = data.datarow;
        }
    }
};
window.addEventListener('message', this.messageHandler);

Each time here are the only differences:

• this.listener has a unique value for each class.
• this.recordId is different each time, it might be this.userId or this.accountId, but so far I'm always setting a property that represents a record's ID.

I'd like to create a function that builds this function. I think this is possible in JavaScript. I seem to remember seeing information on how to do it in one of the many JS resources I used when learning the language. But I can't find the information now.

Ideally, I'd replace the above with something like this:

window.addEventListender('message', generateHandler(this.listener, (datarow) => {
    this.recordId = datarow;
});

How can I do this in JavaScript?

CodePudding user response：

I appreciate the tips in the comments, they helped quite a lot. This is what I ended up writing:

const generateMessageHandler = (listener, callback) => {
    return ({ data, origin }) => {
        if (
            origin === window.location.origin &&
            data.listener === listener &&
            data.event === 'rowclick'
        ) {
            callback(data.datarow);
        }
    };
}

And then calling it with this:

window.addEventListener(
    'message',
    generateMessageHandler(this.rowClickListenerName, (datarow) => {
        this.recordId = datarow;
    })
);

I think I had all the pieces to start with, but something was blocking figuring out the final implementation until the commenters started talking about functions returning functions.

CodePudding user response：

You can certainly return function inside a function in JavaScript, but what's the point in your case?

You can just set the handler to an anonymous function calling your function:

window.addEventListener('message', () => yourFunction(arg1, arg2, arg3));