Changing Button Image On Click (Javascript)

Exactly what the title says. I have tried looking it up but not$$anonymous$$ng seems to work. The last t$$anonymous$$ng I tried was:

if(BID == 1){ B1.GetComponent.() = CubeButton;

W$$anonymous$$ch gives the error: Assets/Inventory.js(96,41): BCE0049: Expression 'self.B1.GetComponent[of UnityEngine.UI.Image]()' cannot be assigned to.

I am just trying to change the button image to an image of a cube when I click on it.