Outlook网页版Office.js报错：item.body非Body实例，prependAsync不存在

开发适配Outlook网页版、Windows及Mac版Outlook 365的插件时，调用item.body.prependAsync方法报错：item.body.prependAsync is not a function。控制台打印item.body结果如下：

{type: undefined, getAsync: ƒ}
getAsync: ƒ wt(e)
type: undefined
[[Prototype]]: Object

HTML代码 #

<!DOCTYPE html>
<html>

<head>
  <title>Addin test</title>
  <script src="https://appsforoffice.microsoft.com/lib/1/hosted/office.js"></script>
  <script>
    let item;

    Office.onReady((info) => {
      if (info.host === Office.HostType.Outlook) {
        item = Office.context.mailbox.item;
        console.log(item.body);
        item.body.prependAsync("text", function (asyncResult) {
          if (asyncResult.status === Office.AsyncResultStatus.Failed) {
            console.log("Action failed with error: " + asyncResult.error.message);
            return;
          }

          console.log(`"${'text'}" prepended to the body.`);
        });
      }
    });
  </script>
</head>

</html>

报错日志 #

Uncaught TypeError: item.body.prependAsync is not a function
    at URLtoHTML/html?et=:14:19
    at appsforoffice.microsoft.com/lib/1/hosted/office.js:76:23268
    at t (appsforoffice.microsoft.com/lib/1/hosted/office.js:76:22669)
    at appsforoffice.microsoft.com/lib/1/hosted/office.js:76:29316
    at c (appsforoffice.microsoft.com/lib/1/hosted/office.js:76:4168)
    at f.waitForFunction (appsforoffice.microsoft.com/lib/1/hosted/office.js:76:4257)
    at e.j [as appReadyCallback] (appsforoffice.microsoft.com/lib/1/hosted/office.js:76:28650)
    at appsforoffice.microsoft.com/lib/1/hosted/outlook-web-16.01.js:20:339988

精简后的manifest.xml #

<?xml version="1.0" encoding="UTF-8"?>
<OfficeApp
  xmlns="http://schemas.microsoft.com/office/appforoffice/1.1"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0"
  xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0"
  xsi:type="MailApp">


  <Id>7218ed19-90f5-4ad6-99e8-8d17ee2556</Id>
  <Version>1.0.0.0</Version>

  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.1" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="URL to HTML" />
        <RequestedHeight>250</RequestedHeight>
      </DesktopSettings>
    </Form>
  </FormSettings>

  <Permissions>ReadWriteItem</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read" />
  </Rule>
  <DisableEntityHighlighting>false</DisableEntityHighlighting>

  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides"
    xsi:type="VersionOverridesV1_0">
    <Requirements>
      <bt:Sets DefaultMinVersion="1.1">
        <bt:Set Name="Mailbox" />
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">

        <DesktopFormFactor>
          <FunctionFile resid="Commands.Url" />

          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgReadGroup">
                <Label resid="GroupLabel" />
                <Control xsi:type="Button" id="msgReadOpenPaneButton">
                  <Label resid="TaskpaneButton.Label" />
                  <Supertip>
                    <Title resid="TaskpaneButton.Label" />
                    <Description resid="TaskpaneButton.Tooltip" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="Icon.16x16" />
                    <bt:Image size="32" resid="Icon.32x32" />
                    <bt:Image size="80" resid="Icon.80x80" />
                  </Icon>

                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
        </DesktopFormFactor>
      </Host>
    </Hosts>

    <Resources>
      <bt:Urls>
        <bt:Url id="Commands.Url" DefaultValue="URL to HTML" />
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="GroupLabel" DefaultValue="Name" />
        <bt:String id="TaskpaneButton.Label" DefaultValue="Action" />
      </bt:ShortStrings>
    </Resources>
  </VersionOverrides>
</OfficeApp>

测试环境为https://outlook.office365.com/网页版，疑问：为何item.body不是预期的Body对象？

核心原因 #

1. 运行模式不匹配：prependAsync是仅支持撰写模式（新建/回复/转发邮件时）的修改类API，而当前插件配置为阅读模式（查看已发送/收件箱邮件时）。阅读模式下的item.body是只读对象，仅提供getAsync方法用于读取内容，不支持任何修改操作。
2. API版本不足：prependAsync要求Mailbox API最低版本为1.3，而你的manifest中声明的最低版本是1.1，版本不满足会导致API无法正常暴露。

具体修改步骤 #

1. 更新manifest配置，切换到撰写模式 #

• 修改<FormSettings>部分，将阅读模式改为撰写模式：

<FormSettings>
  <Form xsi:type="ItemEdit">
    <DesktopSettings>
      <SourceLocation DefaultValue="URL to HTML" />
      <RequestedHeight>250</RequestedHeight>
    </DesktopSettings>
  </Form>
</FormSettings>

• 修改规则部分，匹配撰写模式的邮件：

<Rule xsi:type="RuleCollection" Mode="Or">
  <Rule xsi:type="ItemIs" ItemType="Message" FormType="Edit" />
</Rule>

• 更新ExtensionPoint为撰写模式的命令栏：

<ExtensionPoint xsi:type="MessageComposeCommandSurface">
  <OfficeTab id="TabDefault">
    <Group id="msgComposeGroup">
      <Label resid="GroupLabel" />
      <Control xsi:type="Button" id="msgComposeOpenPaneButton">
        <Label resid="TaskpaneButton.Label" />
        <Supertip>
          <Title resid="TaskpaneButton.Label" />
          <Description resid="TaskpaneButton.Tooltip" />
        </Supertip>
        <Icon>
          <bt:Image size="16" resid="Icon.16x16" />
          <bt:Image size="32" resid="Icon.32x32" />
          <bt:Image size="80" resid="Icon.80x80" />
        </Icon>
      </Control>
    </Group>
  </OfficeTab>
</ExtensionPoint>

2. 升级Mailbox API版本要求 #

• 更新主配置中的版本：

<Requirements>
  <Sets>
    <Set Name="Mailbox" MinVersion="1.3" />
  </Sets>
</Requirements>

• 更新VersionOverrides中的版本：

<Requirements>
  <bt:Sets DefaultMinVersion="1.3">
    <bt:Set Name="Mailbox" />
  </bt:Sets>
</Requirements>

3. 代码中增加模式判断（可选） #

为了避免模式错误导致的异常，可以在代码中先判断当前是否为撰写模式：

Office.onReady((info) => {
  if (info.host === Office.HostType.Outlook) {
    item = Office.context.mailbox.item;
    // 验证是否为撰写模式的邮件
    if (item.isInWriteMode && item.itemType === Office.MailboxEnums.ItemType.Message) {
      item.body.prependAsync("text", function (asyncResult) {
        if (asyncResult.status === Office.AsyncResultStatus.Failed) {
          console.log("Action failed with error: " + asyncResult.error.message);
          return;
        }
        console.log(`"text" prepended to the body.`);
      });
    } else {
      console.log("该操作仅支持在撰写邮件时使用");
    }
  }
});

内容的提问来源于stack exchange，提问作者Jinairu