Event triggered when a text input field becomes active (excluding onfocus) in the FireFox browser

Question

Event triggered when a text input field becomes active (excluding onfocus) in the FireFox browser

I'm currently working on detecting when a text input field is active. Initially, I used the onfocus event, but I encountered an issue where the onblur event would be triggered when the window was no longer in focus, causing unintended consequences in my application. While there's the DOMActivate event that gets fired, Firefox doesn't trigger it for text:input fields.

In a document, only one element can be active at a time. An active element may not necessarily have focus, but an element with focus is always the active element within the document. For instance, if an active element in a window that isn't the foreground window loses its focus, it's no longer considered active.

Fires: button, input:button, input:checkbox, input:file, input:image, input:password, input:radio, input:reset, input:submit

Does not fire: input:text, select, textarea

I also tried using the input event, but this event is only triggered when actual typing occurs in the input box. In my case, I need to capture when the text input field becomes active before any input is typed in and ensure it remains active even when the window is not in focus.

I believe a possible solution could involve using a mutation observer to check if the mutated element becomes the activeElement, but this approach seems like it would require additional overhead. Also, since there isn't an event for scenarios where the active element is lost, it might require extra tracking. Is there a more direct or efficient method to achieve this?

This task involves a Firefox add-on built using addon SDK.

javascript dom firefox-addon-sdk

Answer 1

Answer №1

My experimentation with the mutation observer has produced some useful outcomes, demonstrated in the code snippet below:

var activeInputObserver = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        if(document.activeElement.tagName === "INPUT"){     
            // perform actions specific to the active input field                
        }else{  
            // using 'else' as a focus loss event, making it global instead of per input field  
        }       
    });    
});

var activeInputConfig = { attributes: true, childList: true, characterData: true, subtree: true }
var activeInputTarget = document.querySelector('body'); 

if(target != null){ 
    activeInputObserver.observe(activeInputTarget, activeInputConfig);
}

Utilizing a mutation observer on the body with subtree: true allows monitoring all descendants. However, this approach triggers logic for any active element, necessitating additional tracking variables rather than relying on individual element events. Unfortunately, detecting when an element is no longer active is challenging using this method.

An attempt was made to place a mutation observer on each input field to capture changes upon becoming active; however, this did not trigger mutations upon simply clicking or tabbing into the element:

var activeInputObservers = [];
inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    var activeInputConfig = { attributes: true, childList: true, characterData: true, subtree: true }
    var activeInputTarget = inputField;

    var thisObserver = new MutationObserver(function(mutations) {
    activeInputObservers.push(thisObserver);
        mutations.forEach(function(mutation) {
            console.log("active element:" + JSON.stringify(document.activeElement)   );         
        });    
    });

    thisObserver.observe(activeInputTarget, activeInputConfig);     
}

In this scenario, only typing in the field triggered observable changes, while clicking or tabbing did not. Monitoring changes in the document's activeElement property yields similar challenges in targeting specific elements, leading to executing actions whenever the active element changes without any visible modifications on the input field itself.

Answer 2

My experimentation with the mutation observer has produced some useful outcomes, demonstrated in the code snippet below:

var activeInputObserver = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        if(document.activeElement.tagName === "INPUT"){     
            // perform actions specific to the active input field                
        }else{  
            // using 'else' as a focus loss event, making it global instead of per input field  
        }       
    });    
});

var activeInputConfig = { attributes: true, childList: true, characterData: true, subtree: true }
var activeInputTarget = document.querySelector('body'); 

if(target != null){ 
    activeInputObserver.observe(activeInputTarget, activeInputConfig);
}

Utilizing a mutation observer on the body with subtree: true allows monitoring all descendants. However, this approach triggers logic for any active element, necessitating additional tracking variables rather than relying on individual element events. Unfortunately, detecting when an element is no longer active is challenging using this method.

An attempt was made to place a mutation observer on each input field to capture changes upon becoming active; however, this did not trigger mutations upon simply clicking or tabbing into the element:

var activeInputObservers = [];
inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    var activeInputConfig = { attributes: true, childList: true, characterData: true, subtree: true }
    var activeInputTarget = inputField;

    var thisObserver = new MutationObserver(function(mutations) {
    activeInputObservers.push(thisObserver);
        mutations.forEach(function(mutation) {
            console.log("active element:" + JSON.stringify(document.activeElement)   );         
        });    
    });

    thisObserver.observe(activeInputTarget, activeInputConfig);     
}

In this scenario, only typing in the field triggered observable changes, while clicking or tabbing did not. Monitoring changes in the document's activeElement property yields similar challenges in targeting specific elements, leading to executing actions whenever the active element changes without any visible modifications on the input field itself.

Answer 3

Answer №2

After taking some suggestions from @dandavis and experimenting, I discovered that the document.activeElement remains unchanged when the window loses focus. By implementing a condition in the input fields' blur event, I noticed that it does not propagate up to the window. While this behavior may potentially interfere with other scripts expecting a blur event when the page is in the background, for my addon's purposes, it prevents unintended blurring.

inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    inputField.onfocus = function(){
        //perform actions when input field gains focus
    }   

    inputField.onblur = function(e){

        inputStillActive = false;
        if(this === document.activeElement){
            inputStillActive = true;
            return; 
        }

    }

}

Instead of ending the function early, an alternative approach could involve taking further action. By considering the case where the elements are no longer equal as truly losing focus rather than remaining active but with a blurred window.

In my scenario, I aim to capture input values for use with KeePass autotype. Therefore, I append the current input field's name and id to the window title, resulting in a simplified implementation like this:

var activeInputAttributes = {};

inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    inputField.onfocus = function(){

        activeInputAttributes["name"] = this.getAttribute("name");
        activeInputAttributes["id"] = this.getAttribute("id");

        console.log(activeInputAttributes);

    }   

    inputField.onblur = function(e){

        inputStillActive = false;
        if(this !== document.activeElement){
            activeInputAttributes["name"] = null;
            activeInputAttributes["id"] = null; 
        }

        console.log(activeInputAttributes);

    }

}

The values in activeInputAttributes are set to null only upon leaving the input field, indicating that they remain accessible for auto typing even when the window backgrounded. This approach seems more practical compared to the observation method in my initial response.

Answer 4

After taking some suggestions from @dandavis and experimenting, I discovered that the document.activeElement remains unchanged when the window loses focus. By implementing a condition in the input fields' blur event, I noticed that it does not propagate up to the window. While this behavior may potentially interfere with other scripts expecting a blur event when the page is in the background, for my addon's purposes, it prevents unintended blurring.

inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    inputField.onfocus = function(){
        //perform actions when input field gains focus
    }   

    inputField.onblur = function(e){

        inputStillActive = false;
        if(this === document.activeElement){
            inputStillActive = true;
            return; 
        }

    }

}

Instead of ending the function early, an alternative approach could involve taking further action. By considering the case where the elements are no longer equal as truly losing focus rather than remaining active but with a blurred window.

In my scenario, I aim to capture input values for use with KeePass autotype. Therefore, I append the current input field's name and id to the window title, resulting in a simplified implementation like this:

var activeInputAttributes = {};

inputFields = document.querySelectorAll("input");
for each (var inputField in inputFields){

    inputField.onfocus = function(){

        activeInputAttributes["name"] = this.getAttribute("name");
        activeInputAttributes["id"] = this.getAttribute("id");

        console.log(activeInputAttributes);

    }   

    inputField.onblur = function(e){

        inputStillActive = false;
        if(this !== document.activeElement){
            activeInputAttributes["name"] = null;
            activeInputAttributes["id"] = null; 
        }

        console.log(activeInputAttributes);

    }

}

The values in activeInputAttributes are set to null only upon leaving the input field, indicating that they remain accessible for auto typing even when the window backgrounded. This approach seems more practical compared to the observation method in my initial response.

Event triggered when a text input field becomes active (excluding onfocus) in the FireFox browser

Answer №1

Answer №2

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