Using reduce to extract a result from a JavaScript array

Published on 2020-07-19 • Modified on 2020-07-19

In this snippet, we will see how to extract a result from a JavaScript array using the reduce function and a callback. First, we define two callbacks; they will test if the article is a post or a snippet using an arrow function. Then we use these two "reducers" as the first parameter of the reduce function. The initial value is, of course zero, as we do an accumulation. Open your JavaScript console to check the results.

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/**
 * I am using a JavaScript module to isolate the code of each snippet.
 * In fact it's a Vue.js mixin. Take the code called by the mounted()
 * or the snippetXX() function.
 */
export default {
  methods: {
    snippet103 () {
      const articles = [
        { label: 'Article 1', type: 1 },
        { label: 'Snippet 1', type: 2 },
        { label: 'Snippet 2', type: 2 }
      ]
      const isPost = (accumulator, article) => accumulator + (article.type === 1 ? 1 : 0)
      const isSnippet = (accumulator, article) => accumulator + (article.type === 2 ? 1 : 0)
      console.log('The articles array contains ' + articles.reduce(isPost, 0) + ' post(s).')
      console.log('The articles array contains ' + articles.reduce(isSnippet, 0) + ' snippets(s).')
    }
  },
  mounted () {
    if (this.isArticle(103)) {
      this.snippet103()
    }
  }
}

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