Master Layout

 We can see the placeholders in layout section in sitecore. The same we can do in jss app.

Let me demonstrate the placeholder adding here

Step 1:

Add new placeholders in Layout page

<div className="container">

      <Placeholder name="jss-header" rendering={route} />

    </div>

    <div className="container">

      <Placeholder name="jss-main" rendering={route} />

    </div>

    <div className="container">

      <Placeholder name="jss-main-two" rendering={route} />

    </div>

    <div className="container">

      <Placeholder name="jss-footer" rendering={route} />

    </div>

Step 2:

Add placeholders with display name

 { name: 'jss-main', displayName: 'Main' },

    { name: 'jss-main-tow', displayName: 'Main-Two' },

    { name: 'jss-header', displayName: 'Header' },

    { name: 'jss-footer', displayName: 'Footer' },

Step 3:

Step 4:

Deploy changes to sitecore instance

Open the page in experience editor,

I can see four placeholders here.

Step 4:

Going to create new partial view