javascript barcode scanner

js_barcode_scanner.js

document.addEventListener('DOMContentLoaded', function () {

    if(!window.hasOwnProperty('scan_data')) {
        window.scan_data = [];
        window.scan_prefix_target = null;
    }

    // keystroke speed < 80ms & min total length of 4 chars
    const scan_min_chars = 4, scan_keystroke_window_ms = 80;
    let _scan_timer = window.setTimeout(function() { window.scan_data = []; }, 0);
    const scan_meta_keys = ['Control', 'Alt', 'Meta', 'Tab', 'Escape', 'Shift'];
    document.addEventListener('keydown', function(e) {
        if(scan_meta_keys.indexOf(e.key) !== -1){ return; }
        window.clearTimeout(_scan_timer);
        if(e.key === "Enter" && window.scan_data.length > scan_min_chars) {
            let scannedStr = window.scan_data.join("");
            window.scan_data = [];
            return document.dispatchEvent(new CustomEvent('scanComplete', {detail: scannedStr}))
        } else {
            window.scan_data.push(e.key);
            _scan_timer = window.setTimeout(function() { window.scan_data = []; }, scan_keystroke_window_ms);
        }
    });

    // scanner data received. dispatch
    document.addEventListener('scanComplete', function(e) {
        console.log(e.detail);
        let d = e.detail;

        if (d.startsWith('prefix1')) {
            if (!window.scan_prefix_target) {
                console.log('You must define a prefix target first.');
                return;
            } else {
                console.log('redirect to prefix1 + prefix target id');
            }
        }

        if (d.startsWith('prefix2')) {
            console.log('setting prefix target: prefix2');
            window.scan_ws_target = 'prefix2';
            // do something else....
        }

    });


});