Gatsby-plugin-sitemap generates NaN-NaN-NaN on <lastmod>

Description

When using gatsby-plugin-sitemap to generate sitemap.xml, <lastmod> was not available by default.

Manually adding this would output <lastmod> tags in the final sitemap.xml, but the date were written as NaN-NaN-NaN

Note: Even if we manually uses lastmod: '2020-08-03T01:54:49.000Z' during the serialize below still outputs as NaN

Steps to reproduce

{
      resolve: `gatsby-plugin-sitemap`,
      options: {
        createLinkInHead: true,
        query: `{
          site {
            siteMetadata {
              siteUrl
            }
          }

          allSitePage {
            nodes {
              path
              context {
                updated
              }
            }
          }
        }`,
        resolveSiteUrl: ({ site }) => {
          return site.siteMetadata.siteUrl;
        },
        serialize: ({ site, allSitePage }) =>
          allSitePage.nodes.map((node) => {
            return {
              url: `${site.siteMetadata.siteUrl}${node.path}`,
              changefreq: `daily`,
              priority: 0.7,
              lastmod: `${node.context.updated}`,
            };
          }),
      },
    },

Expected result

Expecting the sitemap to output entries with correct last-modified tags, ie:<lastmod>2020-08-03T01:54:49.000Z</lastmod>

Actual result

<lastmod>NaN-NaN-NaN</lastmod>

Environment

System: OS: macOS 10.15.6 CPU: (8) x64 Intel® Core™ i7-6820HQ CPU @ 2.70GHz Shell: 5.7.1 - /bin/zsh Binaries: Node: 12.17.0 - ~/.nvm/versions/node/v12.17.0/bin/node npm: 6.14.7 - ~/.nvm/versions/node/v12.17.0/bin/npm Languages: Python: 2.7.16 - /usr/bin/python Browsers: Chrome: 84.0.4147.105 Safari: 13.1.2 npmPackages: gatsby: ^2.24.4 => 2.24.4 gatsby-image: ^2.4.13 => 2.4.13 gatsby-plugin-catch-links: ^2.3.11 => 2.3.11 gatsby-plugin-feed-mdx: ^1.0.1 => 1.0.1 gatsby-plugin-google-analytics: ^2.3.11 => 2.3.11 gatsby-plugin-manifest: ^2.4.18 => 2.4.21 gatsby-plugin-mdx: ^1.2.27 => 1.2.27 gatsby-plugin-offline: ^3.2.18 => 3.2.18 gatsby-plugin-preact: ^4.0.9 => 4.0.9 gatsby-plugin-react-helmet: ^3.3.10 => 3.3.10 gatsby-plugin-robots-txt: ^1.5.1 => 1.5.1 gatsby-plugin-s3: ^0.3.3 => 0.3.4 gatsby-plugin-sharp: ^2.6.19 => 2.6.22 gatsby-plugin-sitemap: ^2.4.11 => 2.4.11 gatsby-plugin-styled-components: ^3.3.10 => 3.3.10 gatsby-remark-attr: ^0.1.0 => 0.1.0 gatsby-remark-external-links: 0.0.4 => 0.0.4 gatsby-remark-images: ^3.3.19 => 3.3.19 gatsby-remark-unwrap-images: ^1.0.2 => 1.0.2 gatsby-source-filesystem: ^2.3.20 => 2.3.23 gatsby-transformer-sharp: ^2.5.11 => 2.5.11 npmGlobalPackages: gatsby-cli: 2.12.66

[flikteoh]

@fgambarino Thank you so much. That fixes my problem.

Was wondering why isn’t there any documentation regarding to this on the plugin page itself. Whether is it lastmod or lastmodISO, I felt that it’s somewhat important for users.

Also,

https://support.google.com/webmasters/answer/183668?hl=en Google ignores <priority> and <changefreq> values, so don’t bother adding them. Google reads the <lastmod> value, but if you misrepresent this value, we will stop reading it.

and sorry @vladar I’m unable to create a minimal reproduction for this issue.

In case anyone that came across similar problem, this solved my problem:

via the lastmodISO

    {
      resolve: `gatsby-plugin-sitemap`,
      options: {
        query: `{
          site {
            siteMetadata {
              siteUrl
            }
          }

          allSitePage {
            nodes {
              path
              context {
                updated
              }
            }
          }
        }`,
        resolveSiteUrl: ({ site }) => site.siteMetadata.siteUrl,
        serialize: ({ site, allSitePage }) =>
          allSitePage.nodes.map((node) => {
            const { siteUrl } = site.siteMetadata;
            return {
              url: `${siteUrl}${node.path}`,
              lastmodISO: node.context.updated,
            };
          }),
        createLinkInHead: true,
      },
    },

[github-actions[bot]]

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