Push object including key into array

I want the result to be like

What you've shown after that is invalid (well, okay, you could create something like that, but it's generally a bad idea*). You can create this, though:

[
    {
        pageContext: {
            pageType: "Homepage",
            label: "pageContext"
        }
    }
]

Note that the array contains an object, which contains pageContext.

If that's the result you want, and if _meta is really as shown, just push _meta:

myArray.push(model._meta);

Example:

const myArray = [];

const model = {
  _meta: {
      pageContext: {
          pageType: "Homepage",
          label: "pageContext"
      }
  }
};

myArray.push(model._meta);
console.log(myArray);

If _meta has other things in it that you don't want to push, create a new object:

myArray.push({pageContext: model._meta.pageContext});

Example:

const myArray = [];

const model = {
  _meta: {
      pageContext: {
          pageType: "Homepage",
          label: "pageContext"
      },
      somethingElse: {
           weDontWant: "this"
      }
  }
};

myArray.push({pageContext: model._meta.pageContext});
console.log(myArray);

* If you really want to have an array with a pageContext property on it, you can do that, because arrays are objects:

myArray.pageContext = model._meta.pageContext;

But most of the time, if you think you want to do that, you don't want an array at all, you just want a non-array object.

But what you want is invalid JS. You could obtain something like

[
    { 
        pageContext: {
            pageType: "Homepage",
            label: "pageContext"
        }
    }
]

by using

myArray.push(model._meta);

or something like

[
    { 
        name: 'pageContext',
        value: {
            pageType: "Homepage",
            label: "pageContext"
        }
    }
]

by using

myArray.push({ name: 'pageContext', value: model._meta.pageContext });

[
    {
        pageType: "Homepage",
        label: "pageContext"
    }
]

If you already know that each object is pageContext then push

myArray.push(model._meta.pageContext);