Function parseConstantExpr

test/angular/1.5/angular.js:24998–25009

($parse, context, name, expression, fallback)

}

function parseConstantExpr($parse, context, name, expression, fallback) {
  var parseFn;
  if (isDefined(expression)) {
    parseFn = $parse(expression);
    if (!parseFn.constant) {
      throw ngModelMinErr('constexpr', 'Expected constant expression for `{0}`, but saw ' +
                                   '`{1}`.', name, expression);
    }
    return parseFn(context);
  }
  return fallback;
}

function checkboxInputType(scope, element, attr, ctrl, $sniffer, $browser, $filter, $parse) {
  var trueValue = parseConstantExpr($parse, scope, 'ngTrueValue', attr.ngTrueValue, true);