Adding posts with media using Wordpress API and Javascript library
To set a featured image when creating a post, just provide a featured_media parameter. Example:
wp.media().file("test.jpg").create({ title: "Media Title"}).then(media => { return wp.posts().create({ title: "Your Post Title", content: "Fancy", featured_media: media.id })}).then(post => { // Success}).catch(() => { // Error})To insert the image into the post content, you can put an <img> tag in the content parameter. Example:
wp.media().file("test.jpg").create({ title: "Media Title"}).then(media => { return wp.posts().create({ title: "Hi", content: `<img src="${media.source_url}" />` })})Both of these have been tested against WordPress 5.3.2.I hope this helps!