Vue-pdf implements online preview of PDF files

npm install --save vue-pdf

<template>
    <div>
        <el-row>
            <el-button @click="onPreview" size="small">Preview</el-button>
        </el-row>
        <el-dialog title="Preview Contract Attachment" :visible.sync="viewVisible" center width="60%" @close='closePreview'>
            <el-row :gutter="20">
                <span>Total {{pageCount}} pages, current page {{pdfPage}}</span>
                <el-button type="text" size="mini" @click.stop="previousPage">Previous page</el-button>
                <el-button type="text" size="mini" @click.stop="nextPage">Next page</el-button>
            </el-row>
            <div>
                <pdf :src="src" :page="pdfPage" @num-pages="pageCount = $event" @page-loaded="pdfPage = $event" style="display: inline-block; width: 100%"></pdf>
            </div>
        </el-dialog>
    </div>
</template>
<script>
import pdf from 'vue-pdf'
import store from '@/store/'
export default {
    components:{
        pdf
    },
    data(){
        return {
            viewVisible: false,
            src: null,
            pdfPage : 1,
            pageCount: 0,
            token: store.getters.access_token,
        }
    },
    methods:{
        onPreview(){
            this.src = pdf.createLoadingTask({
                url: 'http://localhost:8082/file/demo.pdf',
                httpHeaders: {Authorization:'Bearer '+ this.token}
            });
            this.src.promise.then(pdf => {
                this.viewVisible = true;
            });
        },
        closePreview(){
            this.pdfPage = 1;
        },
        previousPage(){
            let p = this.pdfPage
            p = p > 1 ? p-1 : this.pageCount
            this.pdfPage = p
        },
        nextPage(){
            let p = this.pdfPage
            p = p < this.pageCount ? p+1 : 1
            this.pdfPage = p
        }
    }
}
</script>

this.src = pdf.createLoadingTask({
    url: 'http://localhost:8082/file/demo.pdf',
});

httpHeaders: {Authorization:'Bearer '+ this.token}

this.src.then(pdf => {
    this.viewVisible = true;
})

TypeError: this.src.then is not a function
    at VueComponent.onPreview (index.vue?6ced:241)
    at click (index.vue?aaff:261)
    at invokeWithErrorHandling (vue.runtime.esm.js?2b0e:1854)
    at VueComponent.invoker (vue.runtime.esm.js?2b0e:2179)
    at invokeWithErrorHandling (vue.runtime.esm.js?2b0e:1854)
    at VueComponent.Vue.$emit (vue.runtime.esm.js?2b0e:3888)
    at VueComponent.handleClick (element-ui.common.js?5c96:9413)
    at invokeWithErrorHandling (vue.runtime.esm.js?2b0e:1854)
    at HTMLButtonElement.invoker (vue.runtime.esm.js?2b0e:2179)
    at HTMLButtonElement.original._wrapper (vue.runtime.esm.js?2b0e:6917)

this.src.promise.then(pdf => {
    this.viewVisible = true;
});