=importJSON support for Sheets, producing keypath/value pairs

Code.js

function IMPORTJSON(url) {
  var response = UrlFetchApp.fetch(url);
  var text = response.getContentText();
  var json = JSON.parse(text);
  
  var output = [];

  var step = function(at, value) {
    if (value instanceof Array) {
      for (var i = 0; i < value.length; i++) {
        var key = `${at}[${i}]`;
        step(key, value[i]);
      }
    } else if (typeof value == "object") {
      for (var k in value) {
        var key = at ? at + "." + k : k;
        step(key, value[k]);
      }
    } else {
      output.push([at, value]);
    }
  }

  step("", json);

  return output;

}