Event is not defined in Firefox

Question

I want to change theme color settings using this code, but it is not working on Firefox. The source code that I used is from this website: https://jonathan-harrell.com/experiment/live-theming-with-css-variables/. Here is my code:

const setValue = (property, value) => {
    if (value) {
        document.documentElement.style.setProperty(`--${property}`, value);

        const input = document.querySelector(`#${property}`);
        if (input) {
            value = value.replace('px', '');
            input.value = value;
        }
    }
};

const setValueFromLocalStorage = property => {
    let value = localStorage.getItem(property);
    setValue(property, value);
};

const setTheme = options => {
    for (let option of Object.keys(options)) {
        const property = option;
        const value = options[option];

        setValue(property, value);
        localStorage.setItem(property, value);
    }
}

const dataThemeButtons = document.querySelectorAll('[data-theme]');

for (let i = 0; i < dataThemeButtons.length; i++) {
    dataThemeButtons[i].addEventListener('click', () => {
        const theme = dataThemeButtons[i].dataset.theme;
        switch (theme) {
            case 'default':
                setTheme({
                    'meta-menu-background-color': '#50463d',
                    'link-color': '#ed1347',
                    'header-menu-color': '#50463d',
                    'header-menu-background-color': '#ffffff',
                    'footer-background-color': '#3c332e',
                    'footer-last-background-color': '#50463d',
                });
            return;
        }
    })
}

document.addEventListener('DOMContentLoaded', () => {
    setValueFromLocalStorage('meta-menu-background-color'),
    setValueFromLocalStorage('link-color'),
    setValueFromLocalStorage('header-menu-color'),
    setValueFromLocalStorage('footer-background-color');
    setValueFromLocalStorage('footer-last-background-color');
});

const handleInputChange = (property, pixels) => {
    document.documentElement.style.setProperty(`--${property}`, `${event.target.value}${pixels ? 'px' : ''}`);
    localStorage.setItem(property, `${event.target.value}${pixels ? 'px' : ''}`);
};

document.querySelector('#meta-menu-background-color').addEventListener('change', event => {
    handleInputChange('meta-menu-background-color', false);
});

In Firefox console I see the error "ReferenceError: event is not defined" on this line:

document.documentElement.style.setProperty(`--${property}`, `${event.target.value}${pixels ? 'px' : ''}`);

It is working fine on Chrome.

Could you help me with this?

Answer 1

The event symbol is global in IE and Chrome, but it's passed as a parameter in Firefox. Thus you need to write your event handler functions with a single parameter (call it event if you want) and then add a preamble line of code to each handler:

function yourHandler(event) {
    event = event || window.event;
    // ...
}