下载qrcode：npm i qrcode
在需要的组件引入：import QRCode from 'qrcode'

组件
<template>
    <view class="container">
        <button type="default" @click="scanCode">扫码</button>
        <view>
            扫码结果：{{qrCodeRes}}
        </view>
    </view>
</template>

<script>
        import Qrcode from 'qrcode'
    export default {
        data() {
            return {
                qrCodeRes: ''
            }
        },
        methods: {
            // 扫码
            scanCode() {
                // #ifdef APP-PLUS
                this.scanCodeAPP()
                // #endif
                
                // #ifdef H5
                this.scanCodeH5()
                // #endif
            },
            // APP直接调用 uni.scanCode 接口
            scanCodeAPP() {
                uni.scanCode({
                    scanType: ['qrCode'],
                    success: (res) => {
                        this.qrCodeRes = res.result
                    }
                })
            },
            // H5通过拉起相机拍照来识别二维码
            scanCodeH5() {
                uni.chooseImage({
                    count: 1,
                    success: imgRes => {
                        Qrcode.qrcode.decode(this.getObjectURL(imgRes.tempFiles[0]))
                        Qrcode.qrcode.callback = (codeRes) => {
                            if (codeRes.indexOf('error') >= 0) {
                                // 二维码识别失败
                                this.qrCodeRes = '不合法二维码：' + codeRes
                            } else {
                                // 二维码识别成功
                                let r = this.decodeStr(codeRes)
                                this.qrCodeRes = r
                            }
                        }
                    }
                })
            },
            // 获取文件地址函数
            getObjectURL(file) {
                var url = null
                if (window.createObjectURL !== undefined) { // basic
                    url = window.createObjectURL(file)
                } else if (window.URL !== undefined) { // mozilla(firefox)
                    url = window.URL.createObjectURL(file)
                } else if (window.webkitURL !== undefined) { // webkit or chrome
                    url = window.webkitURL.createObjectURL(file)
                }
                return url
            },
            // 解码，输出：中文
            decodeStr(str) {
                var out, i, len, c;
                var char2, char3;
                out = "";
                len = str.length;
                i = 0;
                while (i < len) {
                    c = str.charCodeAt(i++);
                    switch (c >> 4) {
                        case 0:
                        case 1:
                        case 2:
                        case 3:
                        case 4:
                        case 5:
                        case 6:
                        case 7:
                            // 0xxxxxxx
                            out += str.charAt(i - 1);
                            break;
                        case 12:
                        case 13:
                            // 110x xxxx 10xx xxxx
                            char2 = str.charCodeAt(i++);
                            out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
                            break;
                        case 14:
                            // 1110 xxxx 10xx xxxx 10xx xxxx
                            char2 = str.charCodeAt(i++);
                            char3 = str.charCodeAt(i++);
                            out += String.fromCharCode(((c & 0x0F) << 12) |
                                ((char2 & 0x3F) << 6) |
                                ((char3 & 0x3F) << 0));
                            break;
                    }
                }
                return out;
            },
        }
    }
</script>

<style>
    .container{
        padding: 10px;
    }
</style>