How to join push an item to array and return it?

[dtvn]

files = {
	link: 'a' 'b'
}

font = { //a
	weight: 300,
	src: push(files.link, {
		url: 'c'
	})
},
{//b
	weight: 300,
	src: files.link {
		url: 'd'
	}
}

In //a the font.src will return number of the array length. In this case is 3
In //b the font.src will return ('a' 'b') 'd'

How do I add the third item to a list ('a' 'b' 'd') without creating nest list (not ('a' 'b') 'd')?