file.js

    addHost() {
        var header = { key: this.hostHeaderKey, value: this.hostHeaderValue };
        if (!this.hasHeader(header)) {
            this.hostHeaders.push(header);
            this.hostHeaderKey = '';
            this.hostHeaderValue = '';
        }
    };
    
    hasHeader(header) {
        // though I'd change hasElement to return boolean, and then just:
        // return this.hasElement(this.hostHeaders, header, 'key');
        var index = this.hasElement(this.hostHeaders, header, 'key');
        // purposfully split fetching the index and the comparison to make it obvious
        // otherwise a random >= 0 at the end could be missed when scanning the code.
        return index >= 0;
    }