title: Javascript concat is not a function
body: <p>Hi this code is not working I get error concat is not a function: how can I fix it?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>var o=[{r:[3,8]},{r:[2,3,4]}];
  undefined
  var R=o.reduce(function(x,y,z){ return x.concat(y.r);})
  VM200964:1 Uncaught TypeError: x.concat is not a function</code></pre>
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