How to use defineProps and defineEmits in vue3.0 grammar sugar

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DefineProps, defineEmits1 and defineProps in grammatical sugar

Get component pass value

☆ ★ import {defineProps, defineEmits, computed, ref} from "vue" / / defineProps () / / adopt ts proprietary declaration There is a default value interface Props {value: number theme: string} const props = withDefaults (defineProps (), {value: 0, theme: 'blue'}) / / non-ts proprietary declaration / / let props = defineProps ({/ / value: Number,// theme: {/ / type: String / / default: 'blue'//} / /}) let width = ref (props.value) function mouseOver (I: number) {width.value = I} function mouseOut () {width.value = props.value} const fontWidth = computed (() = > `width: ${width.value} em `) const themeObj: {[key: string]: string} = {'black':' # 000, 'white':' # f80, 'red':' # f5222d, 'orange':' # 8f0, 'yellow':' # 80f, 'green':' # 0f6, 'blue':' # 08f,} const fontstyle = computed (() = > `color: ${themeObj [props.theme]};`). Rate {position: relative Display: inline-block;}. Rate > span.hollow {position: absolute; display: inline-block; top: 0; left: 0; width: 0; overflow: hidden;} 2, defineEmits

The child component passes to the parent component event

☆ ★ import {defineProps, defineEmits, computed, ref} from "vue" * * ditto code omit / / non-ts declaration / / let emits = defineEmits (['update-rate']) / / function onRate (num) {/ / emits (' update-rate', num) / /} / / adopt ts proprietary declaration Let emits = defineEmits () function onRate (num: number) {emits ('update-rate', num)} / / description of vue grammar sugar in the code above

Some tags can be omitted in the Vue2.X version.

Grammatical sugar refers to adding a method to achieve the same effect without affecting the function so as to facilitate program development.

Vue.js v-bind v-on instructions provide grammatical sugar, which can also be called abbreviations, such as v-bind can omit v-bind.

Just write a colon ":":

V-bind can be omitted as xx:xx, such as