Uncaught TypeError: chrome.extension.getURL is not a function at content.js:269:44

var answer = "cadesplugin_loaded";
            if (isFireFox) {
                answer += "url:";
                answer += browser.extension.getURL("nmcades_plugin_api.js");
            }
            if (isSafari) {
                answer += "url:";
                answer += safari.extension.baseURI + "nmcades_plugin_api.js";
            }
            if (isEdge) {
                answer += "url:";
                answer += chrome.extension.getURL("nmcades_plugin_api.js");
            }