lib/update.js
function $apply(f, value) {
  if (process.env.NODE_ENV !== 'production') {
    assert(isFunction(f), 'Invalid argument f supplied to immutability helper { $apply: f } (expected a function)');
  }
  return f(value);
}
function $apply(f, value) {
  if (process.env.NODE_ENV !== 'production') {
    assert(isFunction(f), 'Invalid argument f supplied to immutability helper { $apply: f } (expected a function)');
  }
  return f(value);
}
function $apply ( f , value ) { if ( process . env . NODE_ENV !== 'production' ) { assert ( isFunction ( f ) , 'Invalid argument f supplied to immutability helper { $apply: f } (expected a function)' ) ; } return f ( value ) ; }
built-in commands
built - in commands