Interpolation and Property Binding

{{ }} is shorthand for a text-node binding

{{ expression }} only ever produces a string, inserted as a text node. It looks like it can go anywhere, but it cannot set a boolean property, cannot set a whole object onto an input, and silently stringifies anything that is not already text:

<h2>{{ user.title }}</h2>
<!-- {{ user }} would render "[object Object]" -->

That last line is a real bug shape, not a hypothetical one: interpolating the object instead of the field it holds compiles fine and renders garbage, because JavaScript's default toString() is the only thing standing between the template and the console.

[prop] sets the DOM property, not the HTML attribute

Property binding writes to the element's DOM property directly, which is why it accepts any expression type — a boolean, a number, an object — not just a string:

<img [src]="user.avatarUrl" [alt]="user.name" />
<button [disabled]="isSaving">Save</button>

This is the one every candidate has to unlearn from plain HTML: disabled="false" as a bare attribute still disables the button, because HTML attributes are presence-based — the string "false" is still a truthy presence. [disabled]="false", in square brackets, binds to the actual boolean property and behaves the way false should. The same trap catches src: interpolating a broken expression into a plain src="{{ user.avatarUrl }}" attribute still issues a request for whatever string comes out, dead link included, while [src] at least binds to the property Angular's change detection actually tracks.

Attribute binding exists for the cases property binding cannot cover

A handful of things genuinely are not DOM properties — colspan, ARIA attributes, aria-label — and for those, [attr.colspan] sets the attribute explicitly rather than a nonexistent property of the same name. Reaching for [attr.x] on something that does have a property (like disabled or src) works but is the wrong tool: it round-trips through the DOM's string-based attribute layer instead of the typed property Angular already exposes.

What interviewers check

Whether the distinction between an attribute and a property is something you can state precisely rather than gesture at, and whether you notice a "disabled button that won't disable" or a "broken image that never updates" for what it actually is: a plain attribute holding a stringified expression where a property binding belongs.