JS function: count number of numer of items in each run (strings of identical items)

get-run-lengths.js

function getRunLengths(array) {
  var runLengths = [];
  var curValue;
  for (var i = 0; i < array.length; i++) {
    if (array[i] === curValue) {
      runLengths[runLengths.length - 1]++;
    }
    else {
      runLengths.push(1);
      curValue = array[i];
    }
  }
  return runLengths;
}