Vue Tip: Props and Context in Setup Method

The setup function in Vue 3 Composition API will take two arguments: props and context.

1<script>
2export default {
3  props: {
4    title: String,
5  },
6  setup(props, context) {
7    /**
8     * Setup does not have the same access to `this` as
9     * the Options API methods.
10     * Thankfully, the setup method accepts a components props
11     * as its first argument
12     */
13    console.log(props)
14
15    /**
16     * Context object exposes three properties of a Vue instance
17     * 1. attrs - a component's attributes
18     * 2. slots - a component's slots
19     * 3. emit - allows us to emit an event from this component
20     */
21    console.log(context)
22    context.emit('eventName')
23  },
24}
25</script>

The first argument in the setup function is the props argument. props are reactive and will be updated when new props are passed in.

Warning

You cannot use ES6 destructuring because it will remove props reactivity. If you want to destructure props you need to use toRefs.

The second argument in the setup function is the context argument. It is a normal JavaScript object that exposes some useful values:

1export default {
2  setup(props, context) {
3    // Attributes (Non-reactive object, equivalent to $attrs)
4    console.log(context.attrs)
5
6    // Slots (Non-reactive object, equivalent to $slots)
7    console.log(context.slots)
8
9    // Emit events (Function, equivalent to $emit)
10    console.log(context.emit)
11
12    // Expose public properties (Function)
13    console.log(context.expose)
14  },
15}

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