获取 canvas 元素的 getContext 方法时，canvas 元素尚未正确绑定。可以通过确保在渲染 PDF 文件之前，canvas 元素已经正确挂载到 DOM 来解决这个问题。

解决方法

1. 确保 pdfCanvas 引用已经绑定到正确的 DOM 元素。
2. 确保在渲染 PDF 文件时，canvas 元素已经挂载。

使用 nextTick 确保在尝试渲染 PDF 文件之前，canvas 元素已经正确挂载

<template><div><button @click="triggerFileInput">选择文件</button><input type="file" ref="fileInput" @change="handleFileChange" style="display: none;" /><div v-if="loading">上传中...</div><div v-if="error" class="error">{{ error }}</div><div v-if="selectedFile" class="pdf-container"><canvas ref="pdfCanvas"></canvas></div></div>
</template>
<script setup>
import { ref, onMounted, nextTick } from 'vue';
import * as pdfjsLib from 'pdfjs-dist';// 设置 pdf.worker.js 路径
pdfjsLib.GlobalWorkerOptions.workerSrc = '/pdf.worker.js';const fileInput = ref(null);
const selectedFile = ref(null);
const loading = ref(false);
const error = ref(null);
const pdfCanvas = ref(null);const triggerFileInput = () => {fileInput.value.click();
};const handleFileChange = async (event) => {const files = event.target.files;if (files.length > 0) {const file = files[0];selectedFile.value = file;// 等待 DOM 更新完成后再渲染 PDFawait nextTick();renderPdf(file);}
};const renderPdf = (file) => {loading.value = true;error.value = null;const reader = new FileReader();reader.readAsArrayBuffer(file);reader.onload = function() {const arrayBuffer = reader.result;const uint8Array = new Uint8Array(arrayBuffer);pdfjsLib.getDocument({ data: uint8Array }).promise.then(pdfDoc => {return pdfDoc.getPage(1).then(page => {const viewport = page.getViewport({ scale: 1.5 });const canvas = pdfCanvas.value;const context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;const renderContext = {canvasContext: context,viewport: viewport};return page.render(renderContext).promise;});}).then(() => {loading.value = false;}).catch(err => {error.value = '加载 PDF 文件失败';console.error('加载 PDF 出错', err);loading.value = false;});};reader.onerror = function(err) {error.value = '读取文件失败';console.error('读取文件出错', err);loading.value = false;};
};
</script>
<style scoped>
button {margin: 10px 0;padding: 10px 20px;font-size: 16px;
}.pdf-container {margin-top: 20px;
}canvas {border: 1px solid #ccc;width: 100%;
}.error {color: red;margin-top: 10px;
}
</style>