- helpers should always be a function, but in #1639 one seems to
be undefined. This was not a problem before 4.6 because helpers
weren't wrapped then.
Now, we must take care only to wrap helpers (when adding
the "lookupProperty" function to the options), if they
are really functions.
Disallow access to prototype properties and methods by default.
Access to properties is always checked via
`Object.prototype.hasOwnProperty.call(parent, propertyName)`.
New runtime options:
- **allowedProtoMethods**: a string-to-boolean map of property-names that are allowed if they are methods of the parent object.
- **allowedProtoProperties**: a string-to-boolean map of property-names that are allowed if they are properties but not methods of the parent object.
```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: ' abc ' })
// result is empty, because trim is defined at String prototype
```
```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: ' abc ' }, {
allowedProtoMethods: {
trim: true
}
})
// result = 'abc'
```
Implementation details: The method now "container.lookupProperty"
handles the prototype-checks and the white-lists. It is used in
- JavaScriptCompiler#nameLookup
- The "lookup"-helper (passed to all helpers as "options.lookupProperty")
- The "lookup" function at the container, which is used for recursive lookups in "compat" mode
Compatibility:
- **Old precompiled templates work with new runtimes**: The "options.lookupPropery"-function is passed to the helper by a wrapper, not by the compiled templated.
- **New templates work with old runtimes**: The template contains a function that is used as fallback if the "lookupProperty"-function cannot be found at the container. However, the runtime-options "allowedProtoProperties" and "allowedProtoMethods" only work with the newest runtime.
BREAKING CHANGE:
- access to prototype properties is forbidden completely by default
Nils Knappmeier