TypeError: Cannot read property '$i18n' of undefined

vue & vue-i18n version

ex: ^2.5.3,^7.3.2

Reproduction Link

Steps to reproduce

• Error: TypeError: Cannot read property ‘$i18n’ of undefined

export default {
    data () {
        const $t = this.$t;
        return {
            msg: $t('msg')
        };
    }
};

• Normal

export default {
    data () {
        const $t = this.$t.bind(this);
        return {
            msg: $t('msg')
        };
    }
};

What is Expected?

export default {
    data () {
        const $t = this.$t;
        return {
            msg: $t('msg')
        };
    }
};

What is actually happening?

This Not equal to component instance

/* @flow */

export default function extend (Vue: any): void {
  Vue.prototype.$t = function (key: Path, ...values: any): TranslateResult {
    const i18n = this.$i18n
    return i18n._t(key, i18n.locale, i18n._getMessages(), this, ...values)
  }

  Vue.prototype.$tc = function (key: Path, choice?: number, ...values: any): TranslateResult {
    const i18n = this.$i18n
    return i18n._tc(key, i18n.locale, i18n._getMessages(), this, choice, ...values)
  }

  Vue.prototype.$te = function (key: Path, locale?: Locale): boolean {
    const i18n = this.$i18n
    return i18n._te(key, i18n.locale, i18n._getMessages(), locale)
  }

  Vue.prototype.$d = function (value: number | Date, ...args: any): DateTimeFormatResult {
    return this.$i18n.d(value, ...args)
  }

  Vue.prototype.$n = function (value: number, ...args: any): NumberFormatResult {
    return this.$i18n.n(value, ...args)
  }
}

[cn-xufei]

Problems still exist. “vue-i18n”: “^8.0.0”

[denisinvader]

it’s very annoying, especially in render functions. I have to write

const $t = key => this.$t(key);
// or
const $t = this.$t.bind(this);

instead of

const { $t, /* necessary props and data */ } = this;