puppeteer 获取iframe

async doFillForm() {
    return await this.page.evaluate(() => {
       let iframe = document.getElementById('frame_id_where_form_is _present');
       let doc = iframe.contentDocument;
       doc.querySelector('#username').value='Bob';
       doc.querySelector('#password').value='pass123';
    });
}

 const  frames = await page.frames();
        console.log('frames',frames)
        const loginFrame = frames.find(
            f => f.name() === 'login_frame');

await loginFrame.waitForSelector('#switcher_plogin');