JavaScript trigger an InputEvent.isTrusted = true

Question

I'm trying to automatize some tasks in JavaScript and I need to use a InputEvent, but when I use normal event, I'm getting event.isTrusted = false and my event is doing nothing. Here is my event code:

var event = new InputEvent('input', {
    bubbles: true,
    cancelable: false,
    data: "a"
}); 

document.getElementById('email').dispatchEvent(event);

This code should put "a" into a textField with id "email", but when event.isTrusted = false, this code is doing nothing. I'm testing it in Chrome Developer Tools in Sources tab with Event Listener Breakpoints (I checked only keyboard>input breakpoint and it shows me all attributes of used event). I checked all attributes from real keyboard click and only thing that is different is event.isTrusted.

What can I change or what can I do to get event.isTrusted = true?

Answer 1

The isTrusted read-only property of the Event interface is a boolean that is true when the event was generated by a user action, and false when the event was created or modified by a script or dispatched via dispatchEvent.

Source: MDN

You may have misunderstood the concept of the Input Event, the event is triggered after the user type in the input. Manually triggering the event will not make the inputs change their values, is the changing of the values that makes the input trigger's the event not the opposite.

If you really want to change the value of the inputs with a custom event you can do something like this:

let TargetInput = document.getElementById('target')
let Button = document.getElementById('btnTrigger');

Button.addEventListener('click',function(e){
    Trigger();
}, false);

TargetInput.addEventListener('input',function(e){
    if(!e.isTrusted){
  //Mannually triggered
  this.value += e.data;
 }
}, false);

function Trigger(){
 var event = new InputEvent('input', {
  bubbles: true,
  cancelable: false,
  data: "a"
 }); 

 TargetInput.dispatchEvent(event);
}

Target: <input type="text" id="target">

<hr>

<button id="btnTrigger">Trigger Event</button>

Answer 2

Any addEventListener call after the following code is executed will have isTrusted set to true.

Element.prototype._addEventListener = Element.prototype.addEventListener;
Element.prototype.addEventListener = function () {
    let args = [...arguments]
    let temp = args[1];
    args[1] = function () {
        let args2 = [...arguments];
        args2[0] = Object.assign({}, args2[0])
        args2[0].isTrusted = true;
        return temp(...args2);
    }
    return this._addEventListener(...args);
}

Note: This is a very "hacky" way to go about doing this.

Answer 3

Unfortunately, you cannot generate event programmatically with isTrusted=true in Google Chrome and others modern browser. See https://developer.mozilla.org/en-US/docs/Web/API/Event/isTrusted

Answer 4

Pupeeteer might help. It generates trusted events.

In browsers, input events could be divided into two big groups: trusted vs. untrusted.

Trusted events: events generated by users interacting with the page, e.g. using a mouse or keyboard. Untrusted event: events generated by Web APIs, e.g. document.createEvent or element.click() methods. Websites can distinguish between these two groups:

• using an Event.isTrusted event flag
• sniffing for accompanying events. For example, every trusted 'click' event is preceded by 'mousedown' and 'mouseup' events.

For automation purposes it’s important to generate trusted events. All input events generated with Puppeteer are trusted and fire proper accompanying events.

Answer 5

I've found it's not possible to set isTrusted to true BUT, depending on your need, a potential solution would be to create a local override in DevTools and remove the conditional in code for the script. This will tell Chrome to use your version (with the isTrusted check removed) instead of the site's JS file.