FieldConfiguration

// Create a number field format
const numberFormat = new NumberFieldFormat ({
  minimumFractionDigits: 2,
  maximumFractionDigits: 4,
  useGrouping: "always"
});

// Create a field configuration object containing the number format
const numFieldConfiguration = new FieldConfiguration ({
  name: "lat", // name of the field in the service
  fieldFormat: numberFormat,
  alias: "Latitude"
});

// Create a date-time field format
const dateTimeFormat = new DateTimeFieldFormat ({
  dateStyle: "medium",
  timeStyle: "short",
  hour12: "never"
});

// Create a field configuration object containing the date format
const dateFieldConfiguration = new FieldConfiguration ({
  name: "collectionDate", // name of the field in the service
  fieldFormat: dateTimeFormat,
  alias: "Date Collected"
});

// Create a feature layer and pass in the field configurations
const featureLayer = new FeatureLayer ({
  url: "url to feature layer",
  outFields: ["*"],
  fieldConfigurations: [numFieldConfiguration, dateFieldConfiguration] // add as many field configurations as needed

});

// Adding a new field configuration
const addNewConfig = (layer, fieldName, alias,
fieldFormat) => {
  const existingConfig = layer.getFieldConfiguration(fieldName);
  if (!existingConfig) {
    const newConfig = new FieldConfiguration ({ name: fieldName, alias, fieldFormat });
    const newConfigs = clone(layer.fieldConfigurations);
    newConfigs.push(newConfig);
    layer.fieldConfigurations = newConfigs;
  }
};

// Updating an existing field configuration
const updateConfig = (layer, fieldName, alias,
fieldFormat) => {
  const existingConfig = layer.getFieldConfiguration(fieldName);
  if (existingConfig) {
    const newConfig = existingConfig.clone();
    newConfig.alias = alias;
    newConfig.fieldFormat = fieldFormat;

    const index = layer.fieldConfigurations.indexOf(existingConfig);
    const newConfigs = clone(layer.fieldConfigurations);
    newConfigs[index] = newConfig;
    layer.fieldConfigurations = newConfigs;
  }
};

// Deleting an existing field configuration
const deleteConfig = (layer, fieldName) => {
  const existingConfig = layer.getFieldConfiguration(fieldName);
  if(existingConfig) {
    const index = layer.fieldConfigurations.indexOf(existingConfig);
    var newConfigs = clone(layer.fieldConfigurations);
    newConfigs.splice(index, 1);
    layer.fieldConfigurations = newConfigs;
 }
};