Javascript: listen for postMessage events from specific iframe

htmliframejavascriptpostmessage

I have multiple iframes in a page. Now I have one message event listener for the page, which gets the messages from all of the iframes. I have a workaround to know from which iframe the message is coming.

I would like to make event listeners for each iframe separately. Is this possible?

Best Solution

You must listen on the global message event of the window object, but you can filter the source iframe using the source property of MessageEvent.

Example:

const childWindow = document.getElementById('test-frame').contentWindow;
window.addEventListener('message', message => {
    if (message.source !== childWindow) {
        return; // Skip message in this event listener
    }

    // ...
});

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Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

I use javascript:void(0).

Three reasons. Encouraging the use of # amongst a team of developers inevitably leads to some using the return value of the function called like this:

function doSomething() {
    //Some code
    return false;
}

But then they forget to use return doSomething() in the onclick and just use doSomething().

A second reason for avoiding # is that the final return false; will not execute if the called function throws an error. Hence the developers have to also remember to handle any error appropriately in the called function.

A third reason is that there are cases where the onclick event property is assigned dynamically. I prefer to be able to call a function or assign it dynamically without having to code the function specifically for one method of attachment or another. Hence my onclick (or on anything) in HTML markup look like this:

onclick="someFunc.call(this)"

onclick="someFunc.apply(this, arguments)"

Using javascript:void(0) avoids all of the above headaches, and I haven't found any examples of a downside.

So if you're a lone developer then you can clearly make your own choice, but if you work as a team you have to either state:

Use href="#", make sure onclick always contains return false; at the end, that any called function does not throw an error and if you attach a function dynamically to the onclick property make sure that as well as not throwing an error it returns false.

Use href="javascript:void(0)"

The second is clearly much easier to communicate.

Javascript – How to check for an empty/undefined/null string in JavaScript

If you just want to check whether there's a truthy value, you can do:

if (strValue) {
    //do something
}

If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against).

if (strValue === "") {
    //...
}

Best Solution

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Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

Javascript – How to check for an empty/undefined/null string in JavaScript

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