test.js

// config
var config = {
  // width, height, etc.
};

function loadAndPrepareData(filter) {
  d3.csv('data.csv', function(error, data) {
    if (error) throw error;

    // empty store
    var massagedData = [];

    // if we pass in a filter, do the highlighting
    // if not, i.e. on initial render, set all highlights to false
    if (filter) {
      // this iterates over each data point
      // I can send you the longhand version of this ternary, but I saw you using it
      // it works this way:
      // var foo = conditionalCheck ? what to do if true : what to do if false
      // so it's strictly equal to:
      // if (conditionalCheck === true) { something } else { somehting else}
      massagedData = data.map(function(d) {
        return { d: d, highlight: d.team === filter ? true : false };
      });
    } else {
      massagedData = data.map(function(d) {
        return { d: d, highlight: false };
      });
    }

    // massagedData is now an array of objects containing:
    // {
    // d: your data,
    // highlight: true or false
    // }

    // @TODO uncomment when you're ready
    // var stratifiedData = d3.stratify()
    // etc. do the rest

    // drawViz(stratifiedData);
  });
}

// this takes in our data now all ready for us
function drawViz(data) {
  // clean up before we draw
  d3.select('#chart').html = '';

  // create d3 layout and hierarchy

  var vSlices = canvas
    .data(vNodes)
    .enter()
    .append('g');

  vSlices
    .append('circle')
    // etc
    // if that's a highlight, full opacity
    // otherwise, 50%
    .attr('opacity', function(d) {
      return d.highlight ? 1 : 0.5;
    });

  // any visual highlighting you want to do, you do this way:
  // .attr('something', function(d) {
  // return d.highlight ? if true : if false;
  //})
}

function handleClickSearch(event) {
  // prevents the page from reloading
  event.preventDefault();

  // stores whatever has been searched
  var currentSearchTerm = document
    .getElementById('mySearchTerm')
    .value.toLowerCase();

  loadAndPrepareData(currentSearchTerm);
}